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teach phi translation of GEPs to simplify geps like 'gep x, 0'. 

This allows us to compile the example from PR5313 into:

LBB1_2:                                                     ## %bb
	incl	%ecx
	movb	%al, (%rsi)
	movslq	%ecx, %rax
	movb	(%rdi,%rax), %al
	testb	%al, %al
	jne	LBB1_2

instead of:

LBB1_2:                                                     ## %bb
	movslq	%eax, %rcx
	incl	%eax
	movb	(%rdi,%rcx), %cl
	movb	%cl, (%rsi)
	movslq	%eax, %rcx
	cmpb	$0, (%rdi,%rcx)
	jne	LBB1_2

llvm-svn: 89981
This commit is contained in:
Chris Lattner 2009-11-27 00:34:38 +00:00
parent 8574aba4ea
commit 5030c6ab21
2 changed files with 33 additions and 3 deletions
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10
llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
View File

@ -20,6 +20,7 @@
#include "llvm/IntrinsicInst.h"
#include "llvm/Function.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
@ -716,7 +717,8 @@ static bool isPHITranslatable(Instruction *Inst) {
/// PHITranslateForPred - Given a computation that satisfied the
/// isPHITranslatable predicate, see if we can translate the computation into
/// the specified predecessor block. If so, return that value.
static Value *PHITranslateForPred(Instruction *Inst, BasicBlock *Pred) {
static Value *PHITranslateForPred(Instruction *Inst, BasicBlock *Pred,
const TargetData *TD) {
if (PHINode *PN = dyn_cast<PHINode>(Inst))
return PN->getIncomingValueForBlock(Pred);
@ -751,7 +753,9 @@ static Value *PHITranslateForPred(Instruction *Inst, BasicBlock *Pred) {
GEPOps.back() = APHIOp = PN->getIncomingValueForBlock(Pred);
}
// TODO: Simplify the GEP to handle 'gep x, 0' -> x etc.
// Simplify the GEP to handle 'gep x, 0' -> x etc.
if (Value *V = SimplifyGEPInst(&GEPOps[0], GEPOps.size(), TD))
return V;
// Scan to see if we have this GEP available.
for (Value::use_iterator UI = APHIOp->use_begin(), E = APHIOp->use_end();
@ -926,7 +930,7 @@ getNonLocalPointerDepFromBB(Value *Pointer, uint64_t PointeeSize,
for (BasicBlock **PI = PredCache->GetPreds(BB); *PI; ++PI) {
BasicBlock *Pred = *PI;
Value *PredPtr = PHITranslateForPred(PtrInst, Pred);
Value *PredPtr = PHITranslateForPred(PtrInst, Pred, TD);
// If PHI translation fails, bail out.
if (PredPtr == 0)

26
llvm/test/Transforms/GVN/rle-phi-translate.ll
View File

@ -86,3 +86,29 @@ bb2:
ret i32 %dv
}
; PR5313
define i32 @test4(i1 %cond, i32* %b, i32* %c) nounwind {
; CHECK: @test4
entry:
br i1 %cond, label %bb, label %bb1
bb:
store i32 4, i32* %b
br label %bb2
bb1:
%c1 = getelementptr i32* %c, i32 7
store i32 82, i32* %c1
br label %bb2
bb2:
%d = phi i32* [ %c, %bb1 ], [ %b, %bb ]
%i = phi i32 [ 7, %bb1 ], [ 0, %bb ]
%d1 = getelementptr i32* %d, i32 %i
%dv = load i32* %d1
; CHECK: %dv = phi i32 [ 82, %bb1 ], [ 4, %bb ]
; CHECK-NOT: load
; CHECK: ret i32 %dv
ret i32 %dv
}