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Revert r219175 - [InstCombine] re-commit r218721 icmp-select-icmp optimization

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This seems to have caused PR21199.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219264 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hans Wennborg
2014-10-08 01:05:57 +00:00
parent 6e36592a73
commit 8315bd8ab0
4 changed files with 9 additions and 152 deletions
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140
lib/Transforms/InstCombine/InstCombineCompares.cpp
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@ -21,7 +21,6 @@
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Target/TargetLibraryInfo.h"
using namespace llvm;
using namespace PatternMatch;
@ -2430,128 +2429,6 @@ static bool swapMayExposeCSEOpportunities(const Value * Op0,
return GlobalSwapBenefits > 0;
}
/// \brief Check that one use is in the same block as the definition and all
/// other uses are in blocks dominated by a given block
///
/// \param DI Definition
/// \param UI Use
/// \param DB Block that must dominate all uses of \p DI outside
/// the parent block
/// \return true when \p UI is the only use of \p DI in the parent block
/// and all other uses of \p DI are in blocks dominated by \p DB.
///
bool InstCombiner::dominatesAllUses(const Instruction *DI,
const Instruction *UI,
const BasicBlock *DB) const {
assert(DI && UI && "Instruction not defined\n");
if (DI->getParent() != UI->getParent())
return false;
// DominatorTree available?
if (!DT)
return false;
for (const User *U : DI->users()) {
auto *Usr = cast<Instruction>(U);
if (Usr != UI && !DT->dominates(DB, Usr->getParent()))
return false;
}
return true;
}
///
/// true when the instruction sequence within a block is select-cmp-br.
///
static bool isChainSelectCmpBranch(const SelectInst *SI) {
const BasicBlock *BB = SI->getParent();
if (!BB)
return false;
auto *BI = dyn_cast_or_null<BranchInst>(BB->getTerminator());
if (!BI || BI->getNumSuccessors() != 2)
return false;
auto *IC = dyn_cast<ICmpInst>(BI->getCondition());
if (!IC || (IC->getOperand(0) != SI && IC->getOperand(1) != SI))
return false;
return true;
}
///
/// \brief True when a select result is replaced by one of its operands
/// in select-icmp sequence. This will eventually result in the elimination
/// of the select.
///
/// \param SI Select instruction
/// \param Icmp Compare instruction
/// \param CI1 'true' when first select operand is equal to RHSC of Icmp
/// \param CI2 'true' when second select operand is equal to RHSC of Icmp
///
/// Notes:
/// - The replacement is global and requires dominator information
/// - The caller is responsible for the actual replacement
///
/// Example:
///
/// entry:
/// %4 = select i1 %3, %C* %0, %C* null
/// %5 = icmp eq %C* %4, null
/// br i1 %5, label %9, label %7
/// ...
/// ; <label>:7 ; preds = %entry
/// %8 = getelementptr inbounds %C* %4, i64 0, i32 0
/// ...
///
/// can be transformed to
///
/// %5 = icmp eq %C* %0, null
/// %6 = select i1 %3, i1 %5, i1 true
/// br i1 %6, label %9, label %7
/// ...
/// ; <label>:7 ; preds = %entry
/// %8 = getelementptr inbounds %C* %0, i64 0, i32 0 // replace by %0!
///
/// Similar when the first operand of the select is a constant or/and
/// the compare is for not equal rather than equal.
///
/// FIXME: Currently the function considers equal compares only. It should be
/// possbile to extend it to not equal compares also.
///
bool InstCombiner::replacedSelectWithOperand(SelectInst *SI,
const ICmpInst *Icmp,
const ConstantInt *CI1,
const ConstantInt *CI2) {
if (isChainSelectCmpBranch(SI) && Icmp->isEquality()) {
// Code sequence is select - icmp.[eq|ne] - br
unsigned ReplaceWithOpd = 0;
if (CI1 && !CI1->isZero())
// The first constant operand of the select and the RHS of
// the compare match, so try to substitute
// the select results with its second operand
// Example:
// %4 = select i1 %3, %C* null, %C* %0
// %5 = icmp eq %C* %4, null
// ==> could replace select with second operand
ReplaceWithOpd = 2;
else if (CI2 && !CI2->isZero())
// Similar when the second operand of the select is a constant
// Example:
// %4 = select i1 %3, %C* %0, %C* null
// %5 = icmp eq %C* %4, null
// ==> could replace select with first operand
ReplaceWithOpd = 1;
if (ReplaceWithOpd) {
// Replace select with operand on else path for EQ compares.
// Replace select with operand on then path for NE compares.
BasicBlock *Succ =
Icmp->getPredicate() == ICmpInst::ICMP_EQ
? SI->getParent()->getTerminator()->getSuccessor(1)
: SI->getParent()->getTerminator()->getSuccessor(0);
if (InstCombiner::dominatesAllUses(SI, Icmp, Succ)) {
SI->replaceAllUsesWith(SI->getOperand(ReplaceWithOpd));
return true;
}
}
}
return false;
}
Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
bool Changed = false;
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
@ -3008,21 +2885,8 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
// fold to a constant (in which case the icmp is replaced with a select
// which will usually simplify) or this is the only user of the
// select (in which case we are trading a select+icmp for a simpler
// select+icmp) or all uses of the select can be replaced based on
// dominance information ("Global cases").
bool Transform = false;
if (Op1 && Op2)
Transform = true;
else if (Op1 || Op2) {
if (LHSI->hasOneUse())
Transform = true;
else
// Global cases
Transform = replacedSelectWithOperand(
cast<SelectInst>(LHSI), &I, dyn_cast_or_null<ConstantInt>(Op1),
dyn_cast_or_null<ConstantInt>(Op2));
}
if (Transform) {
// select+icmp).
if ((Op1 && Op2) || (LHSI->hasOneUse() && (Op1 || Op2))) {
if (!Op1)
Op1 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(1),
RHSC, I.getName());