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if (X == 0 || X == 2) ...where the comparisons and branches are in different blocks... into a switch instruction. This comes up a lot in various programs, and works well with the switch/switch merging code I checked earlier. For example, this testcase: int switchtest(int C) { return C == 0 ? f(123) : C == 1 ? f(3123) : C == 4 ? f(312) : C == 5 ? f(1234): f(444); } is converted into this: switch int %C, label %cond_false.3 [ int 0, label %cond_true.0 int 1, label %cond_true.1 int 4, label %cond_true.2 int 5, label %cond_true.3 ] instead of a whole bunch of conditional branches. Admittedly the code is ugly, and incomplete. To be complete, we need to add br -> switch merging and switch -> br merging. For example, this testcase: struct foo { int Q, R, Z; }; #define A (X->Q+X->R * 123) int test(struct foo *X) { return A == 123 ? X1() : A == 12321 ? X2(): (A == 111 || A == 222) ? X3() : A == 875 ? X4() : X5(); } Gets compiled to this: switch int %tmp.7, label %cond_false.2 [ int 123, label %cond_true.0 int 12321, label %cond_true.1 int 111, label %cond_true.2 int 222, label %cond_true.2 ] ... cond_false.2: ; preds = %entry %tmp.52 = seteq int %tmp.7, 875 ; <bool> [#uses=1] br bool %tmp.52, label %cond_true.3, label %cond_false.3 where the branch could be folded into the switch. This kind of thing occurs *ALL OF THE TIME*, especially in programs like 176.gcc, which is a horrible mess of code. It contains stuff like *shudder*: #define SWITCH_TAKES_ARG(CHAR) \ ( (CHAR) == 'D' \ || (CHAR) == 'U' \ || (CHAR) == 'o' \ || (CHAR) == 'e' \ || (CHAR) == 'u' \ || (CHAR) == 'I' \ || (CHAR) == 'm' \ || (CHAR) == 'L' \ || (CHAR) == 'A' \ || (CHAR) == 'h' \ || (CHAR) == 'z') and #define CONST_OK_FOR_LETTER_P(VALUE, C) \ ((C) == 'I' ? SMALL_INTVAL (VALUE) \ : (C) == 'J' ? SMALL_INTVAL (-(VALUE)) \ : (C) == 'K' ? (unsigned)(VALUE) < 32 \ : (C) == 'L' ? ((VALUE) & 0xffff) == 0 \ : (C) == 'M' ? integer_ok_for_set (VALUE) \ : (C) == 'N' ? (VALUE) < 0 \ : (C) == 'O' ? (VALUE) == 0 \ : (C) == 'P' ? (VALUE) >= 0 \ : 0) and #define LEGITIMIZE_ADDRESS(X,OLDX,MODE,WIN) \ { \ if (GET_CODE (X) == PLUS && CONSTANT_ADDRESS_P (XEXP (X, 1))) \ (X) = gen_rtx (PLUS, SImode, XEXP (X, 0), \ copy_to_mode_reg (SImode, XEXP (X, 1))); \ if (GET_CODE (X) == PLUS && CONSTANT_ADDRESS_P (XEXP (X, 0))) \ (X) = gen_rtx (PLUS, SImode, XEXP (X, 1), \ copy_to_mode_reg (SImode, XEXP (X, 0))); \ if (GET_CODE (X) == PLUS && GET_CODE (XEXP (X, 0)) == MULT) \ (X) = gen_rtx (PLUS, SImode, XEXP (X, 1), \ force_operand (XEXP (X, 0), 0)); \ if (GET_CODE (X) == PLUS && GET_CODE (XEXP (X, 1)) == MULT) \ (X) = gen_rtx (PLUS, SImode, XEXP (X, 0), \ force_operand (XEXP (X, 1), 0)); \ if (GET_CODE (X) == PLUS && GET_CODE (XEXP (X, 0)) == PLUS) \ (X) = gen_rtx (PLUS, Pmode, force_operand (XEXP (X, 0), NULL_RTX),\ XEXP (X, 1)); \ if (GET_CODE (X) == PLUS && GET_CODE (XEXP (X, 1)) == PLUS) \ (X) = gen_rtx (PLUS, Pmode, XEXP (X, 0), \ force_operand (XEXP (X, 1), NULL_RTX)); \ if (GET_CODE (X) == SYMBOL_REF || GET_CODE (X) == CONST \ || GET_CODE (X) == LABEL_REF) \ (X) = legitimize_address (flag_pic, X, 0, 0); \ if (memory_address_p (MODE, X)) \ goto WIN; } and others. These macros get used multiple times of course. These are such lovely candidates for macros, aren't they? :) This code also nicely handles LLVM constructs that look like this: if (isa<CastInst>(I)) ... else if (isa<BranchInst>(I)) ... else if (isa<SetCondInst>(I)) ... else if (isa<UnwindInst>(I)) ... else if (isa<VAArgInst>(I)) ... where the isa can obviously be a dyn_cast as well. Switch instructions are a good thing. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11870 91177308-0d34-0410-b5e6-96231b3b80d8
936 lines
41 KiB
C++
936 lines
41 KiB
C++
//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Peephole optimize the CFG.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/Type.h"
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#include "llvm/Support/CFG.h"
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#include <algorithm>
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#include <functional>
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#include <set>
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using namespace llvm;
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// PropagatePredecessorsForPHIs - This gets "Succ" ready to have the
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// predecessors from "BB". This is a little tricky because "Succ" has PHI
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// nodes, which need to have extra slots added to them to hold the merge edges
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// from BB's predecessors, and BB itself might have had PHI nodes in it. This
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// function returns true (failure) if the Succ BB already has a predecessor that
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// is a predecessor of BB and incoming PHI arguments would not be discernible.
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//
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// Assumption: Succ is the single successor for BB.
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//
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static bool PropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
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assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
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if (!isa<PHINode>(Succ->front()))
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return false; // We can make the transformation, no problem.
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// If there is more than one predecessor, and there are PHI nodes in
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// the successor, then we need to add incoming edges for the PHI nodes
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//
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const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
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// Check to see if one of the predecessors of BB is already a predecessor of
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// Succ. If so, we cannot do the transformation if there are any PHI nodes
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// with incompatible values coming in from the two edges!
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//
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for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); PI != PE; ++PI)
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if (find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) {
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// Loop over all of the PHI nodes checking to see if there are
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// incompatible values coming in.
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for (BasicBlock::iterator I = Succ->begin();
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PHINode *PN = dyn_cast<PHINode>(I); ++I) {
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// Loop up the entries in the PHI node for BB and for *PI if the values
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// coming in are non-equal, we cannot merge these two blocks (instead we
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// should insert a conditional move or something, then merge the
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// blocks).
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int Idx1 = PN->getBasicBlockIndex(BB);
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int Idx2 = PN->getBasicBlockIndex(*PI);
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assert(Idx1 != -1 && Idx2 != -1 &&
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"Didn't have entries for my predecessors??");
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if (PN->getIncomingValue(Idx1) != PN->getIncomingValue(Idx2))
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return true; // Values are not equal...
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}
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}
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// Loop over all of the PHI nodes in the successor BB
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for (BasicBlock::iterator I = Succ->begin();
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PHINode *PN = dyn_cast<PHINode>(I); ++I) {
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Value *OldVal = PN->removeIncomingValue(BB, false);
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assert(OldVal && "No entry in PHI for Pred BB!");
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// If this incoming value is one of the PHI nodes in BB...
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if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
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PHINode *OldValPN = cast<PHINode>(OldVal);
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for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
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End = BBPreds.end(); PredI != End; ++PredI) {
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PN->addIncoming(OldValPN->getIncomingValueForBlock(*PredI), *PredI);
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}
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} else {
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for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
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End = BBPreds.end(); PredI != End; ++PredI) {
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// Add an incoming value for each of the new incoming values...
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PN->addIncoming(OldVal, *PredI);
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}
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}
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}
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return false;
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}
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/// GetIfCondition - Given a basic block (BB) with two predecessors (and
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/// presumably PHI nodes in it), check to see if the merge at this block is due
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/// to an "if condition". If so, return the boolean condition that determines
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/// which entry into BB will be taken. Also, return by references the block
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/// that will be entered from if the condition is true, and the block that will
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/// be entered if the condition is false.
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///
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///
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static Value *GetIfCondition(BasicBlock *BB,
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BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
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assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
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"Function can only handle blocks with 2 predecessors!");
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BasicBlock *Pred1 = *pred_begin(BB);
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BasicBlock *Pred2 = *++pred_begin(BB);
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// We can only handle branches. Other control flow will be lowered to
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// branches if possible anyway.
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if (!isa<BranchInst>(Pred1->getTerminator()) ||
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!isa<BranchInst>(Pred2->getTerminator()))
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return 0;
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BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
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BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
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// Eliminate code duplication by ensuring that Pred1Br is conditional if
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// either are.
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if (Pred2Br->isConditional()) {
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// If both branches are conditional, we don't have an "if statement". In
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// reality, we could transform this case, but since the condition will be
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// required anyway, we stand no chance of eliminating it, so the xform is
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// probably not profitable.
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if (Pred1Br->isConditional())
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return 0;
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std::swap(Pred1, Pred2);
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std::swap(Pred1Br, Pred2Br);
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}
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if (Pred1Br->isConditional()) {
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// If we found a conditional branch predecessor, make sure that it branches
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// to BB and Pred2Br. If it doesn't, this isn't an "if statement".
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if (Pred1Br->getSuccessor(0) == BB &&
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Pred1Br->getSuccessor(1) == Pred2) {
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IfTrue = Pred1;
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IfFalse = Pred2;
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} else if (Pred1Br->getSuccessor(0) == Pred2 &&
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Pred1Br->getSuccessor(1) == BB) {
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IfTrue = Pred2;
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IfFalse = Pred1;
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} else {
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// We know that one arm of the conditional goes to BB, so the other must
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// go somewhere unrelated, and this must not be an "if statement".
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return 0;
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}
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// The only thing we have to watch out for here is to make sure that Pred2
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// doesn't have incoming edges from other blocks. If it does, the condition
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// doesn't dominate BB.
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if (++pred_begin(Pred2) != pred_end(Pred2))
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return 0;
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return Pred1Br->getCondition();
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}
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// Ok, if we got here, both predecessors end with an unconditional branch to
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// BB. Don't panic! If both blocks only have a single (identical)
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// predecessor, and THAT is a conditional branch, then we're all ok!
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if (pred_begin(Pred1) == pred_end(Pred1) ||
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++pred_begin(Pred1) != pred_end(Pred1) ||
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pred_begin(Pred2) == pred_end(Pred2) ||
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++pred_begin(Pred2) != pred_end(Pred2) ||
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*pred_begin(Pred1) != *pred_begin(Pred2))
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return 0;
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// Otherwise, if this is a conditional branch, then we can use it!
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BasicBlock *CommonPred = *pred_begin(Pred1);
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if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
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assert(BI->isConditional() && "Two successors but not conditional?");
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if (BI->getSuccessor(0) == Pred1) {
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IfTrue = Pred1;
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IfFalse = Pred2;
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} else {
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IfTrue = Pred2;
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IfFalse = Pred1;
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}
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return BI->getCondition();
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}
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return 0;
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}
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// If we have a merge point of an "if condition" as accepted above, return true
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// if the specified value dominates the block. We don't handle the true
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// generality of domination here, just a special case which works well enough
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// for us.
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static bool DominatesMergePoint(Value *V, BasicBlock *BB) {
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if (Instruction *I = dyn_cast<Instruction>(V)) {
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BasicBlock *PBB = I->getParent();
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// If this instruction is defined in a block that contains an unconditional
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// branch to BB, then it must be in the 'conditional' part of the "if
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// statement".
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if (isa<BranchInst>(PBB->getTerminator()) &&
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cast<BranchInst>(PBB->getTerminator())->isUnconditional() &&
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cast<BranchInst>(PBB->getTerminator())->getSuccessor(0) == BB)
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return false;
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// We also don't want to allow wierd loops that might have the "if
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// condition" in the bottom of this block.
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if (PBB == BB) return false;
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}
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// Non-instructions all dominate instructions.
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return true;
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}
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// GatherConstantSetEQs - Given a potentially 'or'd together collection of seteq
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// instructions that compare a value against a constant, return the value being
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// compared, and stick the constant into the Values vector.
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static Value *GatherConstantSetEQs(Value *V, std::vector<Constant*> &Values) {
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if (Instruction *Inst = dyn_cast<Instruction>(V))
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if (Inst->getOpcode() == Instruction::SetEQ) {
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if (Constant *C = dyn_cast<Constant>(Inst->getOperand(1))) {
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Values.push_back(C);
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return Inst->getOperand(0);
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} else if (Constant *C = dyn_cast<Constant>(Inst->getOperand(0))) {
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Values.push_back(C);
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return Inst->getOperand(1);
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}
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} else if (Inst->getOpcode() == Instruction::Or) {
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if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
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if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
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if (LHS == RHS)
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return LHS;
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}
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return 0;
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}
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// GatherConstantSetNEs - Given a potentially 'and'd together collection of
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// setne instructions that compare a value against a constant, return the value
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// being compared, and stick the constant into the Values vector.
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static Value *GatherConstantSetNEs(Value *V, std::vector<Constant*> &Values) {
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if (Instruction *Inst = dyn_cast<Instruction>(V))
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if (Inst->getOpcode() == Instruction::SetNE) {
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if (Constant *C = dyn_cast<Constant>(Inst->getOperand(1))) {
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Values.push_back(C);
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return Inst->getOperand(0);
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} else if (Constant *C = dyn_cast<Constant>(Inst->getOperand(0))) {
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Values.push_back(C);
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return Inst->getOperand(1);
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}
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} else if (Inst->getOpcode() == Instruction::Cast) {
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// Cast of X to bool is really a comparison against zero.
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assert(Inst->getType() == Type::BoolTy && "Can only handle bool values!");
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Values.push_back(Constant::getNullValue(Inst->getOperand(0)->getType()));
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return Inst->getOperand(0);
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} else if (Inst->getOpcode() == Instruction::And) {
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if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
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if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
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if (LHS == RHS)
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return LHS;
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}
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return 0;
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}
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/// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
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/// bunch of comparisons of one value against constants, return the value and
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/// the constants being compared.
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static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
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std::vector<Constant*> &Values) {
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if (Cond->getOpcode() == Instruction::Or) {
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CompVal = GatherConstantSetEQs(Cond, Values);
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// Return true to indicate that the condition is true if the CompVal is
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// equal to one of the constants.
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return true;
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} else if (Cond->getOpcode() == Instruction::And) {
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CompVal = GatherConstantSetNEs(Cond, Values);
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// Return false to indicate that the condition is false if the CompVal is
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// equal to one of the constants.
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return false;
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}
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return false;
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}
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/// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and
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/// has no side effects, nuke it. If it uses any instructions that become dead
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/// because the instruction is now gone, nuke them too.
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static void ErasePossiblyDeadInstructionTree(Instruction *I) {
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if (isInstructionTriviallyDead(I)) {
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std::vector<Value*> Operands(I->op_begin(), I->op_end());
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I->getParent()->getInstList().erase(I);
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for (unsigned i = 0, e = Operands.size(); i != e; ++i)
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if (Instruction *OpI = dyn_cast<Instruction>(Operands[i]))
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ErasePossiblyDeadInstructionTree(OpI);
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}
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}
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/// SafeToMergeTerminators - Return true if it is safe to merge these two
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/// terminator instructions together.
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///
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static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
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if (SI1 == SI2) return false; // Can't merge with self!
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// It is not safe to merge these two switch instructions if they have a common
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// successor, and if that successor has a PHI node, and if that PHI node has
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// conflicting incoming values from the two switch blocks.
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BasicBlock *SI1BB = SI1->getParent();
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BasicBlock *SI2BB = SI2->getParent();
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std::set<BasicBlock*> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
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for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
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if (SI1Succs.count(*I))
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for (BasicBlock::iterator BBI = (*I)->begin();
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PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI)
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if (PN->getIncomingValueForBlock(SI1BB) !=
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PN->getIncomingValueForBlock(SI2BB))
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return false;
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return true;
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}
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/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
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/// now be entries in it from the 'NewPred' block. The values that will be
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/// flowing into the PHI nodes will be the same as those coming in from
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/// ExistPred, and existing predecessor of Succ.
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static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
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BasicBlock *ExistPred) {
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assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
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succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
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if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
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for (BasicBlock::iterator I = Succ->begin();
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PHINode *PN = dyn_cast<PHINode>(I); ++I) {
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Value *V = PN->getIncomingValueForBlock(ExistPred);
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PN->addIncoming(V, NewPred);
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}
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}
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// SimplifyCFG - This function is used to do simplification of a CFG. For
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// example, it adjusts branches to branches to eliminate the extra hop, it
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// eliminates unreachable basic blocks, and does other "peephole" optimization
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// of the CFG. It returns true if a modification was made.
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//
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// WARNING: The entry node of a function may not be simplified.
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//
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bool llvm::SimplifyCFG(BasicBlock *BB) {
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bool Changed = false;
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Function *M = BB->getParent();
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assert(BB && BB->getParent() && "Block not embedded in function!");
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assert(BB->getTerminator() && "Degenerate basic block encountered!");
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assert(&BB->getParent()->front() != BB && "Can't Simplify entry block!");
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// Remove basic blocks that have no predecessors... which are unreachable.
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if (pred_begin(BB) == pred_end(BB) ||
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*pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(BB)) {
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//cerr << "Removing BB: \n" << BB;
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// Loop through all of our successors and make sure they know that one
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// of their predecessors is going away.
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for_each(succ_begin(BB), succ_end(BB),
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std::bind2nd(std::mem_fun(&BasicBlock::removePredecessor), BB));
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while (!BB->empty()) {
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Instruction &I = BB->back();
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|
// If this instruction is used, replace uses with an arbitrary
|
|
// constant value. Because control flow can't get here, we don't care
|
|
// what we replace the value with. Note that since this block is
|
|
// unreachable, and all values contained within it must dominate their
|
|
// uses, that all uses will eventually be removed.
|
|
if (!I.use_empty())
|
|
// Make all users of this instruction reference the constant instead
|
|
I.replaceAllUsesWith(Constant::getNullValue(I.getType()));
|
|
|
|
// Remove the instruction from the basic block
|
|
BB->getInstList().pop_back();
|
|
}
|
|
M->getBasicBlockList().erase(BB);
|
|
return true;
|
|
}
|
|
|
|
// Check to see if we can constant propagate this terminator instruction
|
|
// away...
|
|
Changed |= ConstantFoldTerminator(BB);
|
|
|
|
// Check to see if this block has no non-phi instructions and only a single
|
|
// successor. If so, replace references to this basic block with references
|
|
// to the successor.
|
|
succ_iterator SI(succ_begin(BB));
|
|
if (SI != succ_end(BB) && ++SI == succ_end(BB)) { // One succ?
|
|
|
|
BasicBlock::iterator BBI = BB->begin(); // Skip over phi nodes...
|
|
while (isa<PHINode>(*BBI)) ++BBI;
|
|
|
|
if (BBI->isTerminator()) { // Terminator is the only non-phi instruction!
|
|
BasicBlock *Succ = *succ_begin(BB); // There is exactly one successor
|
|
|
|
if (Succ != BB) { // Arg, don't hurt infinite loops!
|
|
// If our successor has PHI nodes, then we need to update them to
|
|
// include entries for BB's predecessors, not for BB itself.
|
|
// Be careful though, if this transformation fails (returns true) then
|
|
// we cannot do this transformation!
|
|
//
|
|
if (!PropagatePredecessorsForPHIs(BB, Succ)) {
|
|
//cerr << "Killing Trivial BB: \n" << BB;
|
|
std::string OldName = BB->getName();
|
|
|
|
std::vector<BasicBlock*>
|
|
OldSuccPreds(pred_begin(Succ), pred_end(Succ));
|
|
|
|
// Move all PHI nodes in BB to Succ if they are alive, otherwise
|
|
// delete them.
|
|
while (PHINode *PN = dyn_cast<PHINode>(&BB->front()))
|
|
if (PN->use_empty())
|
|
BB->getInstList().erase(BB->begin()); // Nuke instruction...
|
|
else {
|
|
// The instruction is alive, so this means that Succ must have
|
|
// *ONLY* had BB as a predecessor, and the PHI node is still valid
|
|
// now. Simply move it into Succ, because we know that BB
|
|
// strictly dominated Succ.
|
|
BB->getInstList().remove(BB->begin());
|
|
Succ->getInstList().push_front(PN);
|
|
|
|
// We need to add new entries for the PHI node to account for
|
|
// predecessors of Succ that the PHI node does not take into
|
|
// account. At this point, since we know that BB dominated succ,
|
|
// this means that we should any newly added incoming edges should
|
|
// use the PHI node as the value for these edges, because they are
|
|
// loop back edges.
|
|
|
|
for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
|
|
if (OldSuccPreds[i] != BB)
|
|
PN->addIncoming(PN, OldSuccPreds[i]);
|
|
}
|
|
|
|
// Everything that jumped to BB now goes to Succ...
|
|
BB->replaceAllUsesWith(Succ);
|
|
|
|
// Delete the old basic block...
|
|
M->getBasicBlockList().erase(BB);
|
|
|
|
if (!OldName.empty() && !Succ->hasName()) // Transfer name if we can
|
|
Succ->setName(OldName);
|
|
|
|
//cerr << "Function after removal: \n" << M;
|
|
return true;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// If this is a returning block with only PHI nodes in it, fold the return
|
|
// instruction into any unconditional branch predecessors.
|
|
if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
|
|
BasicBlock::iterator BBI = BB->getTerminator();
|
|
if (BBI == BB->begin() || isa<PHINode>(--BBI)) {
|
|
// Find predecessors that end with unconditional branches.
|
|
std::vector<BasicBlock*> UncondBranchPreds;
|
|
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
|
|
TerminatorInst *PTI = (*PI)->getTerminator();
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
|
|
if (BI->isUnconditional())
|
|
UncondBranchPreds.push_back(*PI);
|
|
}
|
|
|
|
// If we found some, do the transformation!
|
|
if (!UncondBranchPreds.empty()) {
|
|
while (!UncondBranchPreds.empty()) {
|
|
BasicBlock *Pred = UncondBranchPreds.back();
|
|
UncondBranchPreds.pop_back();
|
|
Instruction *UncondBranch = Pred->getTerminator();
|
|
// Clone the return and add it to the end of the predecessor.
|
|
Instruction *NewRet = RI->clone();
|
|
Pred->getInstList().push_back(NewRet);
|
|
|
|
// If the return instruction returns a value, and if the value was a
|
|
// PHI node in "BB", propagate the right value into the return.
|
|
if (NewRet->getNumOperands() == 1)
|
|
if (PHINode *PN = dyn_cast<PHINode>(NewRet->getOperand(0)))
|
|
if (PN->getParent() == BB)
|
|
NewRet->setOperand(0, PN->getIncomingValueForBlock(Pred));
|
|
// Update any PHI nodes in the returning block to realize that we no
|
|
// longer branch to them.
|
|
BB->removePredecessor(Pred);
|
|
Pred->getInstList().erase(UncondBranch);
|
|
}
|
|
|
|
// If we eliminated all predecessors of the block, delete the block now.
|
|
if (pred_begin(BB) == pred_end(BB))
|
|
// We know there are no successors, so just nuke the block.
|
|
M->getBasicBlockList().erase(BB);
|
|
|
|
return true;
|
|
}
|
|
}
|
|
} else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->begin())) {
|
|
// Check to see if the first instruction in this block is just an unwind.
|
|
// If so, replace any invoke instructions which use this as an exception
|
|
// destination with call instructions.
|
|
//
|
|
std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
|
|
while (!Preds.empty()) {
|
|
BasicBlock *Pred = Preds.back();
|
|
if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
|
|
if (II->getUnwindDest() == BB) {
|
|
// Insert a new branch instruction before the invoke, because this
|
|
// is now a fall through...
|
|
BranchInst *BI = new BranchInst(II->getNormalDest(), II);
|
|
Pred->getInstList().remove(II); // Take out of symbol table
|
|
|
|
// Insert the call now...
|
|
std::vector<Value*> Args(II->op_begin()+3, II->op_end());
|
|
CallInst *CI = new CallInst(II->getCalledValue(), Args,
|
|
II->getName(), BI);
|
|
// If the invoke produced a value, the Call now does instead
|
|
II->replaceAllUsesWith(CI);
|
|
delete II;
|
|
Changed = true;
|
|
}
|
|
|
|
Preds.pop_back();
|
|
}
|
|
|
|
// If this block is now dead, remove it.
|
|
if (pred_begin(BB) == pred_end(BB)) {
|
|
// We know there are no successors, so just nuke the block.
|
|
M->getBasicBlockList().erase(BB);
|
|
return true;
|
|
}
|
|
|
|
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->begin())) {
|
|
// If the only instruction in this block is a switch instruction, see if we
|
|
// can fold the switch instruction into a switch in a predecessor block.
|
|
std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
|
|
while (!Preds.empty()) {
|
|
BasicBlock *Pred = Preds.back();
|
|
Preds.pop_back();
|
|
|
|
// If the two blocks are switching on the same value, we can merge this
|
|
// switch into the predecessor's switch.
|
|
if (SwitchInst *PSI = dyn_cast<SwitchInst>(Pred->getTerminator()))
|
|
if (PSI->getCondition() == SI->getCondition() &&
|
|
SafeToMergeTerminators(SI, PSI)) {
|
|
// Figure out which 'cases' to copy from SI to PSI.
|
|
std::vector<std::pair<Constant*, BasicBlock*> > Cases;
|
|
BasicBlock *NewDefault = 0;
|
|
if (PSI->getDefaultDest() == BB) {
|
|
// If this is the default destination from PSI, only the edges in SI
|
|
// that don't occur in PSI, or that branch to BB will be activated.
|
|
std::set<Constant*> PSIHandled;
|
|
for (unsigned i = 1, e = PSI->getNumSuccessors(); i != e; ++i)
|
|
if (PSI->getSuccessor(i) != BB)
|
|
PSIHandled.insert(PSI->getCaseValue(i));
|
|
else {
|
|
// This entry will be replaced.
|
|
PSI->removeCase(i);
|
|
--i; --e;
|
|
}
|
|
|
|
NewDefault = SI->getDefaultDest();
|
|
for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
|
|
Constant *C = SI->getCaseValue(i);
|
|
if (!PSIHandled.count(C))
|
|
Cases.push_back(std::make_pair(C, SI->getSuccessor(i)));
|
|
}
|
|
|
|
} else {
|
|
// If this is not the default destination from PSI, only the edges
|
|
// in SI that occur in PSI with a destination of BB will be
|
|
// activated.
|
|
std::set<Constant*> PSIHandled;
|
|
for (unsigned i = 1, e = PSI->getNumSuccessors(); i != e; ++i)
|
|
if (PSI->getSuccessor(i) == BB) {
|
|
// We know that BB doesn't have any PHI nodes in it, so just
|
|
// drop the edges.
|
|
PSIHandled.insert(PSI->getCaseValue(i));
|
|
PSI->removeCase(i);
|
|
--i; --e;
|
|
}
|
|
|
|
// Okay, now we know which constants were sent to BB from the
|
|
// predecessor. Figure out where they will all go now.
|
|
for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
|
|
Constant *C = SI->getCaseValue(i);
|
|
if (PSIHandled.count(C)) {
|
|
// If this is one we are capable of getting...
|
|
Cases.push_back(std::make_pair(C, SI->getSuccessor(i)));
|
|
PSIHandled.erase(C); // This constant is taken care of
|
|
}
|
|
}
|
|
|
|
// If there are any constants vectored to BB that SI doesn't handle,
|
|
// they must go to the default destination of SI.
|
|
for (std::set<Constant*>::iterator I = PSIHandled.begin(),
|
|
E = PSIHandled.end(); I != E; ++I)
|
|
Cases.push_back(std::make_pair(*I, SI->getDefaultDest()));
|
|
}
|
|
|
|
// Okay, at this point, we know which cases need to be added to the
|
|
// PSI switch and which destinations they go to. If PSI needs its
|
|
// default destination changed, NewDefault is set. Start changing
|
|
// stuff now.
|
|
if (NewDefault) {
|
|
AddPredecessorToBlock(NewDefault, Pred, BB);
|
|
PSI->setSuccessor(0, NewDefault);
|
|
}
|
|
|
|
// Okay, add all of the cases now.
|
|
for (unsigned i = 0, e = Cases.size(); i != e; ++i) {
|
|
AddPredecessorToBlock(Cases[i].second, Pred, BB);
|
|
PSI->addCase(Cases[i].first, Cases[i].second);
|
|
}
|
|
|
|
// Okay, last check. If BB is still a successor of PSI, then we must
|
|
// have an infinite loop case. If so, add an infinitely looping block
|
|
// to handle the case to preserve the behavior of the code.
|
|
BasicBlock *InfLoopBlock = 0;
|
|
for (unsigned i = 0, e = PSI->getNumSuccessors(); i != e; ++i)
|
|
if (PSI->getSuccessor(i) == BB) {
|
|
if (InfLoopBlock == 0) {
|
|
// Insert it at the end of the loop, because it's either code,
|
|
// or it won't matter if it's hot. :)
|
|
InfLoopBlock = new BasicBlock("infloop", BB->getParent());
|
|
new BranchInst(InfLoopBlock, InfLoopBlock);
|
|
}
|
|
PSI->setSuccessor(i, InfLoopBlock);
|
|
}
|
|
|
|
Changed = true;
|
|
}
|
|
}
|
|
|
|
// If we removed all predecessors of this block, recursively call
|
|
// SimplifyCFG to remove it.
|
|
if (pred_begin(BB) == pred_end(BB))
|
|
return SimplifyCFG(BB);
|
|
}
|
|
|
|
// Merge basic blocks into their predecessor if there is only one distinct
|
|
// pred, and if there is only one distinct successor of the predecessor, and
|
|
// if there are no PHI nodes.
|
|
//
|
|
pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
|
|
BasicBlock *OnlyPred = *PI++;
|
|
for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
|
|
if (*PI != OnlyPred) {
|
|
OnlyPred = 0; // There are multiple different predecessors...
|
|
break;
|
|
}
|
|
|
|
BasicBlock *OnlySucc = 0;
|
|
if (OnlyPred && OnlyPred != BB && // Don't break self loops
|
|
OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) {
|
|
// Check to see if there is only one distinct successor...
|
|
succ_iterator SI(succ_begin(OnlyPred)), SE(succ_end(OnlyPred));
|
|
OnlySucc = BB;
|
|
for (; SI != SE; ++SI)
|
|
if (*SI != OnlySucc) {
|
|
OnlySucc = 0; // There are multiple distinct successors!
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (OnlySucc) {
|
|
//cerr << "Merging: " << BB << "into: " << OnlyPred;
|
|
TerminatorInst *Term = OnlyPred->getTerminator();
|
|
|
|
// Resolve any PHI nodes at the start of the block. They are all
|
|
// guaranteed to have exactly one entry if they exist, unless there are
|
|
// multiple duplicate (but guaranteed to be equal) entries for the
|
|
// incoming edges. This occurs when there are multiple edges from
|
|
// OnlyPred to OnlySucc.
|
|
//
|
|
while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
|
|
PN->replaceAllUsesWith(PN->getIncomingValue(0));
|
|
BB->getInstList().pop_front(); // Delete the phi node...
|
|
}
|
|
|
|
// Delete the unconditional branch from the predecessor...
|
|
OnlyPred->getInstList().pop_back();
|
|
|
|
// Move all definitions in the successor to the predecessor...
|
|
OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
|
|
|
|
// Make all PHI nodes that referred to BB now refer to Pred as their
|
|
// source...
|
|
BB->replaceAllUsesWith(OnlyPred);
|
|
|
|
std::string OldName = BB->getName();
|
|
|
|
// Erase basic block from the function...
|
|
M->getBasicBlockList().erase(BB);
|
|
|
|
// Inherit predecessors name if it exists...
|
|
if (!OldName.empty() && !OnlyPred->hasName())
|
|
OnlyPred->setName(OldName);
|
|
|
|
return true;
|
|
}
|
|
|
|
// If there is a single predecessor for this block, and if this block is a
|
|
// simple value comparison block (ie, contains X == C), see if we can fold
|
|
// this comparison into the comparison in our predecessor block, making the
|
|
// predecessor block terminator into a switch (or adding cases to a
|
|
// preexisting switch).
|
|
if (OnlyPred) {
|
|
if (SetCondInst *SCI = dyn_cast<SetCondInst>(BB->begin()))
|
|
if (SCI->getOpcode() == Instruction::SetEQ && SCI->hasOneUse() &&
|
|
isa<BranchInst>(SCI->use_back()) &&
|
|
SCI->getNext() == cast<BranchInst>(SCI->use_back())) {
|
|
// Okay, we know we have a block containing (only) a seteq and a
|
|
// conditional branch instruction. If an integer value is being
|
|
// compared, if the comparison value is a constant, then check the
|
|
// predecessor.
|
|
BranchInst *BBBr = cast<BranchInst>(BB->getTerminator());
|
|
Value *CompVal = SCI->getOperand(0);
|
|
if (ConstantInt *CVal = dyn_cast<ConstantInt>(SCI->getOperand(1))) {
|
|
// We can do the merge if the predecessor contains either a
|
|
// conditional branch or a switch instruction which is operating on
|
|
// the CompVal.
|
|
if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator())){
|
|
// If it is a branch, then it must be a conditional branch,
|
|
// otherwise we would have merged it in before. We can only handle
|
|
// this if the block we are looking at is the 'false' branch.
|
|
assert(BI->isConditional() &&
|
|
"Should have previously merged blocks!");
|
|
if (SetCondInst *PredSCC= dyn_cast<SetCondInst>(BI->getCondition()))
|
|
if (PredSCC->getOperand(0) == CompVal &&
|
|
PredSCC->getOpcode() == Instruction::SetEQ &&
|
|
isa<ConstantInt>(PredSCC->getOperand(1)) &&
|
|
BB == BI->getSuccessor(1) &&
|
|
SafeToMergeTerminators(BI, BBBr)) {
|
|
// If the constants being compared are the same, then the
|
|
// comparison in this block could never come true.
|
|
if (SCI->getOperand(1) == PredSCC->getOperand(1)) {
|
|
// Tell the block to skip over us, making us dead.
|
|
BI->setSuccessor(1, BBBr->getSuccessor(1));
|
|
AddPredecessorToBlock(BBBr->getSuccessor(1), OnlyPred, BB);
|
|
return SimplifyCFG(BB);
|
|
}
|
|
|
|
// Otherwise, create the switch instruction!
|
|
SwitchInst *SI = new SwitchInst(CompVal, BBBr->getSuccessor(1),
|
|
BI);
|
|
// Add the edge from our predecessor, and remove the
|
|
// predecessors (now obsolete branch instruction). This makes
|
|
// the current block dead.
|
|
SI->addCase(cast<Constant>(PredSCC->getOperand(1)),
|
|
BI->getSuccessor(0));
|
|
OnlyPred->getInstList().erase(BI);
|
|
if (PredSCC->use_empty())
|
|
PredSCC->getParent()->getInstList().erase(PredSCC);
|
|
|
|
// Add our case...
|
|
SI->addCase(cast<Constant>(SCI->getOperand(1)),
|
|
BBBr->getSuccessor(0));
|
|
|
|
AddPredecessorToBlock(BBBr->getSuccessor(0), OnlyPred, BB);
|
|
AddPredecessorToBlock(BBBr->getSuccessor(1), OnlyPred, BB);
|
|
|
|
//std::cerr << "Formed Switch: " << SI;
|
|
|
|
// Made a big change! Now this block is dead, so remove it.
|
|
return SimplifyCFG(BB);
|
|
}
|
|
|
|
} else if (SwitchInst *SI =
|
|
dyn_cast<SwitchInst>(OnlyPred->getTerminator())) {
|
|
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
|
|
if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
|
|
// Change br (X == 0 | X == 1), T, F into a switch instruction.
|
|
if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
|
|
Instruction *Cond = cast<Instruction>(BI->getCondition());
|
|
// If this is a bunch of seteq's or'd together, or if it's a bunch of
|
|
// 'setne's and'ed together, collect them.
|
|
Value *CompVal = 0;
|
|
std::vector<Constant*> Values;
|
|
bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
|
|
if (CompVal && CompVal->getType()->isInteger()) {
|
|
// There might be duplicate constants in the list, which the switch
|
|
// instruction can't handle, remove them now.
|
|
std::sort(Values.begin(), Values.end());
|
|
Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
|
|
|
|
// Figure out which block is which destination.
|
|
BasicBlock *DefaultBB = BI->getSuccessor(1);
|
|
BasicBlock *EdgeBB = BI->getSuccessor(0);
|
|
if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
|
|
|
|
// Create the new switch instruction now.
|
|
SwitchInst *New = new SwitchInst(CompVal, DefaultBB, BI);
|
|
|
|
// Add all of the 'cases' to the switch instruction.
|
|
for (unsigned i = 0, e = Values.size(); i != e; ++i)
|
|
New->addCase(Values[i], EdgeBB);
|
|
|
|
// We added edges from PI to the EdgeBB. As such, if there were any
|
|
// PHI nodes in EdgeBB, they need entries to be added corresponding to
|
|
// the number of edges added.
|
|
for (BasicBlock::iterator BBI = EdgeBB->begin();
|
|
PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI) {
|
|
Value *InVal = PN->getIncomingValueForBlock(*PI);
|
|
for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
|
|
PN->addIncoming(InVal, *PI);
|
|
}
|
|
|
|
// Erase the old branch instruction.
|
|
(*PI)->getInstList().erase(BI);
|
|
|
|
// Erase the potentially condition tree that was used to computed the
|
|
// branch condition.
|
|
ErasePossiblyDeadInstructionTree(Cond);
|
|
return true;
|
|
}
|
|
}
|
|
|
|
// If there is a trivial two-entry PHI node in this basic block, and we can
|
|
// eliminate it, do so now.
|
|
if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
|
|
if (PN->getNumIncomingValues() == 2) {
|
|
// Ok, this is a two entry PHI node. Check to see if this is a simple "if
|
|
// statement", which has a very simple dominance structure. Basically, we
|
|
// are trying to find the condition that is being branched on, which
|
|
// subsequently causes this merge to happen. We really want control
|
|
// dependence information for this check, but simplifycfg can't keep it up
|
|
// to date, and this catches most of the cases we care about anyway.
|
|
//
|
|
BasicBlock *IfTrue, *IfFalse;
|
|
if (Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse)) {
|
|
//std::cerr << "FOUND IF CONDITION! " << *IfCond << " T: "
|
|
// << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
|
|
|
|
// Figure out where to insert instructions as necessary.
|
|
BasicBlock::iterator AfterPHIIt = BB->begin();
|
|
while (isa<PHINode>(AfterPHIIt)) ++AfterPHIIt;
|
|
|
|
BasicBlock::iterator I = BB->begin();
|
|
while (PHINode *PN = dyn_cast<PHINode>(I)) {
|
|
++I;
|
|
|
|
// If we can eliminate this PHI by directly computing it based on the
|
|
// condition, do so now. We can't eliminate PHI nodes where the
|
|
// incoming values are defined in the conditional parts of the branch,
|
|
// so check for this.
|
|
//
|
|
if (DominatesMergePoint(PN->getIncomingValue(0), BB) &&
|
|
DominatesMergePoint(PN->getIncomingValue(1), BB)) {
|
|
Value *TrueVal =
|
|
PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
|
|
Value *FalseVal =
|
|
PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
|
|
|
|
// FIXME: when we have a 'select' statement, we can be completely
|
|
// generic and clean here and let the instcombine pass clean up
|
|
// after us, by folding the select instructions away when possible.
|
|
//
|
|
if (TrueVal == FalseVal) {
|
|
// Degenerate case...
|
|
PN->replaceAllUsesWith(TrueVal);
|
|
BB->getInstList().erase(PN);
|
|
Changed = true;
|
|
} else if (isa<ConstantBool>(TrueVal) &&
|
|
isa<ConstantBool>(FalseVal)) {
|
|
if (TrueVal == ConstantBool::True) {
|
|
// The PHI node produces the same thing as the condition.
|
|
PN->replaceAllUsesWith(IfCond);
|
|
} else {
|
|
// The PHI node produces the inverse of the condition. Insert a
|
|
// "NOT" instruction, which is really a XOR.
|
|
Value *InverseCond =
|
|
BinaryOperator::createNot(IfCond, IfCond->getName()+".inv",
|
|
AfterPHIIt);
|
|
PN->replaceAllUsesWith(InverseCond);
|
|
}
|
|
BB->getInstList().erase(PN);
|
|
Changed = true;
|
|
} else if (isa<ConstantInt>(TrueVal) && isa<ConstantInt>(FalseVal)){
|
|
// If this is a PHI of two constant integers, we insert a cast of
|
|
// the boolean to the integer type in question, giving us 0 or 1.
|
|
// Then we multiply this by the difference of the two constants,
|
|
// giving us 0 if false, and the difference if true. We add this
|
|
// result to the base constant, giving us our final value. We
|
|
// rely on the instruction combiner to eliminate many special
|
|
// cases, like turning multiplies into shifts when possible.
|
|
std::string Name = PN->getName(); PN->setName("");
|
|
Value *TheCast = new CastInst(IfCond, TrueVal->getType(),
|
|
Name, AfterPHIIt);
|
|
Constant *TheDiff = ConstantExpr::get(Instruction::Sub,
|
|
cast<Constant>(TrueVal),
|
|
cast<Constant>(FalseVal));
|
|
Value *V = TheCast;
|
|
if (TheDiff != ConstantInt::get(TrueVal->getType(), 1))
|
|
V = BinaryOperator::create(Instruction::Mul, TheCast,
|
|
TheDiff, TheCast->getName()+".scale",
|
|
AfterPHIIt);
|
|
if (!cast<Constant>(FalseVal)->isNullValue())
|
|
V = BinaryOperator::create(Instruction::Add, V, FalseVal,
|
|
V->getName()+".offs", AfterPHIIt);
|
|
PN->replaceAllUsesWith(V);
|
|
BB->getInstList().erase(PN);
|
|
Changed = true;
|
|
} else if (isa<ConstantInt>(FalseVal) &&
|
|
cast<Constant>(FalseVal)->isNullValue()) {
|
|
// If the false condition is an integral zero value, we can
|
|
// compute the PHI by multiplying the condition by the other
|
|
// value.
|
|
std::string Name = PN->getName(); PN->setName("");
|
|
Value *TheCast = new CastInst(IfCond, TrueVal->getType(),
|
|
Name+".c", AfterPHIIt);
|
|
Value *V = BinaryOperator::create(Instruction::Mul, TrueVal,
|
|
TheCast, Name, AfterPHIIt);
|
|
PN->replaceAllUsesWith(V);
|
|
BB->getInstList().erase(PN);
|
|
Changed = true;
|
|
} else if (isa<ConstantInt>(TrueVal) &&
|
|
cast<Constant>(TrueVal)->isNullValue()) {
|
|
// If the true condition is an integral zero value, we can compute
|
|
// the PHI by multiplying the inverse condition by the other
|
|
// value.
|
|
std::string Name = PN->getName(); PN->setName("");
|
|
Value *NotCond = BinaryOperator::createNot(IfCond, Name+".inv",
|
|
AfterPHIIt);
|
|
Value *TheCast = new CastInst(NotCond, TrueVal->getType(),
|
|
Name+".inv", AfterPHIIt);
|
|
Value *V = BinaryOperator::create(Instruction::Mul, FalseVal,
|
|
TheCast, Name, AfterPHIIt);
|
|
PN->replaceAllUsesWith(V);
|
|
BB->getInstList().erase(PN);
|
|
Changed = true;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
return Changed;
|
|
}
|