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Kill some duplicated code for removing unreachable BBs.

Browse Source 
This moves removeUnreachableBlocksFromFn from SimplifyCFGPass.cpp
to Utils/Local.cpp and uses it to replace the implementation of
llvm::removeUnreachableBlocks, which appears to do a strict subset
of what removeUnreachableBlocksFromFn does.

Differential Revision: http://llvm-reviews.chandlerc.com/D1334

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188119 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Peter Collingbourne 2013-08-09 22:47:24 +00:00
parent aaae6e9cb8
commit 835738ce54
3 changed files with 152 additions and 174 deletions
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165
lib/Transforms/Scalar/SimplifyCFGPass.cpp
View File

@ -66,161 +66,6 @@ FunctionPass *llvm::createCFGSimplificationPass() {
return new CFGSimplifyPass(); return new CFGSimplifyPass();
} }
/// changeToUnreachable - Insert an unreachable instruction before the specified
/// instruction, making it and the rest of the code in the block dead.
static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
BasicBlock *BB = I->getParent();
// Loop over all of the successors, removing BB's entry from any PHI
// nodes.
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
(*SI)->removePredecessor(BB);
// Insert a call to llvm.trap right before this. This turns the undefined
// behavior into a hard fail instead of falling through into random code.
if (UseLLVMTrap) {
Function *TrapFn =
Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
CallTrap->setDebugLoc(I->getDebugLoc());
}
new UnreachableInst(I->getContext(), I);
// All instructions after this are dead.
BasicBlock::iterator BBI = I, BBE = BB->end();
while (BBI != BBE) {
if (!BBI->use_empty())
BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
BB->getInstList().erase(BBI++);
}
}
/// changeToCall - Convert the specified invoke into a normal call.
static void changeToCall(InvokeInst *II) {
SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II);
NewCall->takeName(II);
NewCall->setCallingConv(II->getCallingConv());
NewCall->setAttributes(II->getAttributes());
NewCall->setDebugLoc(II->getDebugLoc());
II->replaceAllUsesWith(NewCall);
// Follow the call by a branch to the normal destination.
BranchInst::Create(II->getNormalDest(), II);
// Update PHI nodes in the unwind destination
II->getUnwindDest()->removePredecessor(II->getParent());
II->eraseFromParent();
}
static bool markAliveBlocks(BasicBlock *BB,
SmallPtrSet<BasicBlock*, 128> &Reachable) {
SmallVector<BasicBlock*, 128> Worklist;
Worklist.push_back(BB);
Reachable.insert(BB);
bool Changed = false;
do {
BB = Worklist.pop_back_val();
// Do a quick scan of the basic block, turning any obviously unreachable
// instructions into LLVM unreachable insts. The instruction combining pass
// canonicalizes unreachable insts into stores to null or undef.
for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
if (CI->doesNotReturn()) {
// If we found a call to a no-return function, insert an unreachable
// instruction after it. Make sure there isn't *already* one there
// though.
++BBI;
if (!isa<UnreachableInst>(BBI)) {
// Don't insert a call to llvm.trap right before the unreachable.
changeToUnreachable(BBI, false);
Changed = true;
}
break;
}
}
// Store to undef and store to null are undefined and used to signal that
// they should be changed to unreachable by passes that can't modify the
// CFG.
if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
// Don't touch volatile stores.
if (SI->isVolatile()) continue;
Value *Ptr = SI->getOperand(1);
if (isa<UndefValue>(Ptr) ||
(isa<ConstantPointerNull>(Ptr) &&
SI->getPointerAddressSpace() == 0)) {
changeToUnreachable(SI, true);
Changed = true;
break;
}
}
}
// Turn invokes that call 'nounwind' functions into ordinary calls.
if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
Value *Callee = II->getCalledValue();
if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
changeToUnreachable(II, true);
Changed = true;
} else if (II->doesNotThrow()) {
if (II->use_empty() && II->onlyReadsMemory()) {
// jump to the normal destination branch.
BranchInst::Create(II->getNormalDest(), II);
II->getUnwindDest()->removePredecessor(II->getParent());
II->eraseFromParent();
} else
changeToCall(II);
Changed = true;
}
}
Changed |= ConstantFoldTerminator(BB, true);
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
if (Reachable.insert(*SI))
Worklist.push_back(*SI);
} while (!Worklist.empty());
return Changed;
}
/// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
/// if they are in a dead cycle. Return true if a change was made, false
/// otherwise.
static bool removeUnreachableBlocksFromFn(Function &F) {
SmallPtrSet<BasicBlock*, 128> Reachable;
bool Changed = markAliveBlocks(F.begin(), Reachable);
// If there are unreachable blocks in the CFG...
if (Reachable.size() == F.size())
return Changed;
assert(Reachable.size() < F.size());
NumSimpl += F.size()-Reachable.size();
// Loop over all of the basic blocks that are not reachable, dropping all of
// their internal references...
for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
if (Reachable.count(BB))
continue;
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
if (Reachable.count(*SI))
(*SI)->removePredecessor(BB);
BB->dropAllReferences();
}
for (Function::iterator I = ++F.begin(); I != F.end();)
if (!Reachable.count(I))
I = F.getBasicBlockList().erase(I);
else
++I;
return true;
}
/// mergeEmptyReturnBlocks - If we have more than one empty (other than phi /// mergeEmptyReturnBlocks - If we have more than one empty (other than phi
/// node) return blocks, merge them together to promote recursive block merging. /// node) return blocks, merge them together to promote recursive block merging.
static bool mergeEmptyReturnBlocks(Function &F) { static bool mergeEmptyReturnBlocks(Function &F) {
@ -325,7 +170,7 @@ static bool iterativelySimplifyCFG(Function &F, const TargetTransformInfo &TTI,
bool CFGSimplifyPass::runOnFunction(Function &F) { bool CFGSimplifyPass::runOnFunction(Function &F) {
const TargetTransformInfo &TTI = getAnalysis<TargetTransformInfo>(); const TargetTransformInfo &TTI = getAnalysis<TargetTransformInfo>();
const DataLayout *TD = getAnalysisIfAvailable<DataLayout>(); const DataLayout *TD = getAnalysisIfAvailable<DataLayout>();
bool EverChanged = removeUnreachableBlocksFromFn(F); bool EverChanged = removeUnreachableBlocks(F);
EverChanged |= mergeEmptyReturnBlocks(F); EverChanged |= mergeEmptyReturnBlocks(F);
EverChanged |= iterativelySimplifyCFG(F, TTI, TD); EverChanged |= iterativelySimplifyCFG(F, TTI, TD);
@ -333,16 +178,16 @@ bool CFGSimplifyPass::runOnFunction(Function &F) {
if (!EverChanged) return false; if (!EverChanged) return false;
// iterativelySimplifyCFG can (rarely) make some loops dead. If this happens, // iterativelySimplifyCFG can (rarely) make some loops dead. If this happens,
// removeUnreachableBlocksFromFn is needed to nuke them, which means we should // removeUnreachableBlocks is needed to nuke them, which means we should
// iterate between the two optimizations. We structure the code like this to // iterate between the two optimizations. We structure the code like this to
// avoid reruning iterativelySimplifyCFG if the second pass of // avoid reruning iterativelySimplifyCFG if the second pass of
// removeUnreachableBlocksFromFn doesn't do anything. // removeUnreachableBlocks doesn't do anything.
if (!removeUnreachableBlocksFromFn(F)) if (!removeUnreachableBlocks(F))
return true; return true;
do { do {
EverChanged = iterativelySimplifyCFG(F, TTI, TD); EverChanged = iterativelySimplifyCFG(F, TTI, TD);
EverChanged |= removeUnreachableBlocksFromFn(F); EverChanged |= removeUnreachableBlocks(F);
} while (EverChanged); } while (EverChanged);
return true; return true;

147
lib/Transforms/Utils/Local.cpp
View File

@ -16,6 +16,7 @@
#include "llvm/ADT/DenseMap.h" #include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h" #include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/Dominators.h" #include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/InstructionSimplify.h" #include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/Analysis/MemoryBuiltins.h"
@ -43,6 +44,8 @@
#include "llvm/Support/raw_ostream.h" #include "llvm/Support/raw_ostream.h"
using namespace llvm; using namespace llvm;
STATISTIC(NumRemoved, "Number of unreachable basic blocks removed");
//===----------------------------------------------------------------------===// //===----------------------------------------------------------------------===//
// Local constant propagation. // Local constant propagation.
// //
@ -1121,33 +1124,153 @@ bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
return true; return true;
} }
bool llvm::removeUnreachableBlocks(Function &F) { /// changeToUnreachable - Insert an unreachable instruction before the specified
SmallPtrSet<BasicBlock*, 16> Reachable; /// instruction, making it and the rest of the code in the block dead.
static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
BasicBlock *BB = I->getParent();
// Loop over all of the successors, removing BB's entry from any PHI
// nodes.
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
(*SI)->removePredecessor(BB);
// Insert a call to llvm.trap right before this. This turns the undefined
// behavior into a hard fail instead of falling through into random code.
if (UseLLVMTrap) {
Function *TrapFn =
Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
CallTrap->setDebugLoc(I->getDebugLoc());
}
new UnreachableInst(I->getContext(), I);
// All instructions after this are dead.
BasicBlock::iterator BBI = I, BBE = BB->end();
while (BBI != BBE) {
if (!BBI->use_empty())
BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
BB->getInstList().erase(BBI++);
}
}
/// changeToCall - Convert the specified invoke into a normal call.
static void changeToCall(InvokeInst *II) {
SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II);
NewCall->takeName(II);
NewCall->setCallingConv(II->getCallingConv());
NewCall->setAttributes(II->getAttributes());
NewCall->setDebugLoc(II->getDebugLoc());
II->replaceAllUsesWith(NewCall);
// Follow the call by a branch to the normal destination.
BranchInst::Create(II->getNormalDest(), II);
// Update PHI nodes in the unwind destination
II->getUnwindDest()->removePredecessor(II->getParent());
II->eraseFromParent();
}
static bool markAliveBlocks(BasicBlock *BB,
SmallPtrSet<BasicBlock*, 128> &Reachable) {
SmallVector<BasicBlock*, 128> Worklist; SmallVector<BasicBlock*, 128> Worklist;
Worklist.push_back(&F.getEntryBlock()); Worklist.push_back(BB);
Reachable.insert(&F.getEntryBlock()); Reachable.insert(BB);
bool Changed = false;
do { do {
BasicBlock *BB = Worklist.pop_back_val(); BB = Worklist.pop_back_val();
// Do a quick scan of the basic block, turning any obviously unreachable
// instructions into LLVM unreachable insts. The instruction combining pass
// canonicalizes unreachable insts into stores to null or undef.
for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
if (CI->doesNotReturn()) {
// If we found a call to a no-return function, insert an unreachable
// instruction after it. Make sure there isn't *already* one there
// though.
++BBI;
if (!isa<UnreachableInst>(BBI)) {
// Don't insert a call to llvm.trap right before the unreachable.
changeToUnreachable(BBI, false);
Changed = true;
}
break;
}
}
// Store to undef and store to null are undefined and used to signal that
// they should be changed to unreachable by passes that can't modify the
// CFG.
if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
// Don't touch volatile stores.
if (SI->isVolatile()) continue;
Value *Ptr = SI->getOperand(1);
if (isa<UndefValue>(Ptr) ||
(isa<ConstantPointerNull>(Ptr) &&
SI->getPointerAddressSpace() == 0)) {
changeToUnreachable(SI, true);
Changed = true;
break;
}
}
}
// Turn invokes that call 'nounwind' functions into ordinary calls.
if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
Value *Callee = II->getCalledValue();
if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
changeToUnreachable(II, true);
Changed = true;
} else if (II->doesNotThrow()) {
if (II->use_empty() && II->onlyReadsMemory()) {
// jump to the normal destination branch.
BranchInst::Create(II->getNormalDest(), II);
II->getUnwindDest()->removePredecessor(II->getParent());
II->eraseFromParent();
} else
changeToCall(II);
Changed = true;
}
}
Changed |= ConstantFoldTerminator(BB, true);
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
if (Reachable.insert(*SI)) if (Reachable.insert(*SI))
Worklist.push_back(*SI); Worklist.push_back(*SI);
} while (!Worklist.empty()); } while (!Worklist.empty());
return Changed;
}
/// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
/// if they are in a dead cycle. Return true if a change was made, false
/// otherwise.
bool llvm::removeUnreachableBlocks(Function &F) {
SmallPtrSet<BasicBlock*, 128> Reachable;
bool Changed = markAliveBlocks(F.begin(), Reachable);
// If there are unreachable blocks in the CFG...
if (Reachable.size() == F.size()) if (Reachable.size() == F.size())
return false; return Changed;
assert(Reachable.size() < F.size()); assert(Reachable.size() < F.size());
for (Function::iterator I = llvm::next(F.begin()), E = F.end(); I != E; ++I) { NumRemoved += F.size()-Reachable.size();
if (Reachable.count(I))
// Loop over all of the basic blocks that are not reachable, dropping all of
// their internal references...
for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
if (Reachable.count(BB))
continue; continue;
for (succ_iterator SI = succ_begin(I), SE = succ_end(I); SI != SE; ++SI) for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
if (Reachable.count(*SI)) if (Reachable.count(*SI))
(*SI)->removePredecessor(I); (*SI)->removePredecessor(BB);
I->dropAllReferences(); BB->dropAllReferences();
} }
for (Function::iterator I = llvm::next(F.begin()), E=F.end(); I != E;) for (Function::iterator I = ++F.begin(); I != F.end();)
if (!Reachable.count(I)) if (!Reachable.count(I))
I = F.getBasicBlockList().erase(I); I = F.getBasicBlockList().erase(I);
else else

14
test/Instrumentation/DataFlowSanitizer/args-unreachable-bb.ll
View File

@ -1,8 +1,8 @@
; RUN: opt < %s -dfsan -verify -dfsan-args-abi -S | FileCheck %s ; RUN: opt < %s -dfsan -verify -dfsan-args-abi -S | FileCheck %s
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128" target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
define i8 @unreachable_bb() { ; CHECK-LABEL: @unreachable_bb1
; CHECK: @unreachable_bb define i8 @unreachable_bb1() {
; CHECK: ret { i8, i16 } { i8 1, i16 0 } ; CHECK: ret { i8, i16 } { i8 1, i16 0 }
; CHECK-NOT: bb2: ; CHECK-NOT: bb2:
; CHECK-NOT: bb3: ; CHECK-NOT: bb3:
@ -18,3 +18,13 @@ bb3:
bb4: bb4:
br label %bb3 br label %bb3
} }
declare void @abort() noreturn
; CHECK-LABEL: @unreachable_bb2
define i8 @unreachable_bb2() {
call void @abort() noreturn
; CHECK-NOT: i8 12
; CHECK: unreachable
ret i8 12
}