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licm is wasting time hoisting constant foldable operations,

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instead of hoisting them, just fold them away.  This occurs in the
testcase for PR8041, for example.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112669 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-08-31 23:00:16 +00:00
parent 232ab949d5
commit 2ac6e2354a
3 changed files with 38 additions and 10 deletions
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20
lib/Transforms/Scalar/LICM.cpp
View File

@ -36,11 +36,11 @@
#include "llvm/DerivedTypes.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Instructions.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AliasSetTracker.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Transforms/Utils/Local.h"
@ -353,6 +353,18 @@ void LICM::HoistRegion(DomTreeNode *N) {
for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ) {
Instruction &I = *II++;
// Try constant folding this instruction. If all the operands are
// constants, it is technically hoistable, but it would be better to just
// fold it.
if (Constant *C = ConstantFoldInstruction(&I)) {
DEBUG(dbgs() << "LICM folding inst: " << I << " --> " << *C << '\n');
CurAST->copyValue(&I, C);
CurAST->deleteValue(&I);
I.replaceAllUsesWith(C);
I.eraseFromParent();
continue;
}
// Try hoisting the instruction out to the preheader. We can only do this
// if all of the operands of the instruction are loop invariant and if it
// is safe to hoist the instruction.
@ -360,7 +372,7 @@ void LICM::HoistRegion(DomTreeNode *N) {
if (isLoopInvariantInst(I) && canSinkOrHoistInst(I) &&
isSafeToExecuteUnconditionally(I))
hoist(I);
}
}
const std::vector<DomTreeNode*> &Children = N->getChildren();
for (unsigned i = 0, e = Children.size(); i != e; ++i)

16
test/Transforms/LICM/hoisting.ll
View File

@ -48,3 +48,19 @@ Out: ; preds = %Loop
%C = sub i32 %A, %B ; <i32> [#uses=1]
ret i32 %C
}
; This loop invariant instruction should be constant folded, not hoisted.
define i32 @test3(i1 %c) {
; CHECK: define i32 @test3
; CHECK: call void @foo2(i32 6)
%A = load i32* @X ; <i32> [#uses=2]
br label %Loop
Loop:
%B = add i32 4, 2 ; <i32> [#uses=2]
call void @foo2( i32 %B )
br i1 %c, label %Loop, label %Out
Out: ; preds = %Loop
%C = sub i32 %A, %B ; <i32> [#uses=1]
ret i32 %C
}

12
test/Transforms/LICM/scalar_promote.ll
View File

@ -1,4 +1,6 @@
; RUN: opt < %s -licm -S | FileCheck %s
target datalayout = "E-p:64:64:64-a0:0:8-f32:32:32-f64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-v64:64:64-v128:128:128"
@X = global i32 7 ; <i32*> [#uses=4]
define void @test1(i32 %i) {
@ -32,23 +34,21 @@ Entry:
br label %Loop
; CHECK: @test2
; CHECK: Entry:
; CHECK-NEXT: %X1 = getelementptr i32* @X, i64 0
; CHECK-NEXT: %X2 = getelementptr i32* @X, i64 0
; CHECK-NEXT: %X1.promoted = load i32* %X1
; CHECK-NEXT: %.promoted = load i32* getelementptr inbounds (i32* @X, i64 1)
; CHECK-NEXT: br label %Loop
Loop: ; preds = %Loop, %0
%X1 = getelementptr i32* @X, i64 0 ; <i32*> [#uses=1]
%X1 = getelementptr i32* @X, i64 1 ; <i32*> [#uses=1]
%A = load i32* %X1 ; <i32> [#uses=1]
%V = add i32 %A, 1 ; <i32> [#uses=1]
%X2 = getelementptr i32* @X, i64 0 ; <i32*> [#uses=1]
%X2 = getelementptr i32* @X, i64 1 ; <i32*> [#uses=1]
store i32 %V, i32* %X2
br i1 false, label %Loop, label %Exit
Exit: ; preds = %Loop
ret void
; CHECK: Exit:
; CHECK-NEXT: store i32 %V, i32* %X1
; CHECK-NEXT: store i32 %V, i32* getelementptr inbounds (i32* @X, i64 1)
; CHECK-NEXT: ret void
}