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Teach memdep to phi translate bitcasts. This allows us to compile

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the example in GCC PR16799 to:

LBB1_2:                                                     ## %bb1
	movl	%eax, %eax
	subq	%rax, %rdi
	movq	%rdi, (%rcx)
	movl	(%rdi), %eax
	testl	%eax, %eax
	je	LBB1_2

instead of:

LBB1_2:                                                     ## %bb1
	movl	(%rdi), %ecx
	subq	%rcx, %rdi
	movq	%rdi, (%rax)
	cmpl	$0, (%rdi)
	je	LBB1_2



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89978 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-11-26 23:41:07 +00:00
parent 38028653a9
commit cc3d0eb483
3 changed files with 53 additions and 5 deletions
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30
lib/Analysis/MemoryDependenceAnalysis.cpp
View File

@ -690,10 +690,15 @@ static bool isPHITranslatable(Instruction *Inst) {
if (isa<PHINode>(Inst))
return true;
// TODO: BITCAST, GEP.
// ...
// We can handle bitcast of a PHI, but the PHI needs to be in the same block
// as the bitcast.
if (BitCastInst *BC = dyn_cast<BitCastInst>(Inst))
if (PHINode *PN = dyn_cast<PHINode>(BC->getOperand(0)))
if (PN->getParent() == BC->getParent())
return true;
// TODO: GEP, ...
// cerr << "MEMDEP: Could not PHI translate: " << *Pointer;
// if (isa<BitCastInst>(PtrInst) || isa<GetElementPtrInst>(PtrInst))
// cerr << "OP:\t\t\t\t" << *PtrInst->getOperand(0);
@ -708,6 +713,25 @@ static Value *PHITranslateForPred(Instruction *Inst, BasicBlock *Pred) {
if (PHINode *PN = dyn_cast<PHINode>(Inst))
return PN->getIncomingValueForBlock(Pred);
if (BitCastInst *BC = dyn_cast<BitCastInst>(Inst)) {
PHINode *BCPN = cast<PHINode>(BC->getOperand(0));
Value *PHIIn = BCPN->getIncomingValueForBlock(Pred);
// Constants are trivial to phi translate.
if (Constant *C = dyn_cast<Constant>(PHIIn))
return ConstantExpr::getBitCast(C, BC->getType());
// Otherwise we have to see if a bitcasted version of the incoming pointer
// is available. If so, we can use it, otherwise we have to fail.
for (Value::use_iterator UI = PHIIn->use_begin(), E = PHIIn->use_end();
UI != E; ++UI) {
if (BitCastInst *BCI = dyn_cast<BitCastInst>(*UI))
if (BCI->getType() == BC->getType())
return BCI;
}
return 0;
}
return 0;
}

2
lib/Target/README.txt
View File

@ -1284,8 +1284,6 @@ http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35287 [LPRE crit edge splitting]
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34677 (licm does this, LPRE crit edge)
llvm-gcc t2.c -S -o - -O0 -emit-llvm | llvm-as | opt -mem2reg -simplifycfg -gvn | llvm-dis
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16799 [BITCAST PHI TRANS]
//===---------------------------------------------------------------------===//
Type based alias analysis:

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

@ -4,6 +4,7 @@ target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f3
target triple = "i386-apple-darwin7"
define i32 @test1(i32* %b, i32* %c) nounwind {
; CHECK: @test1
entry:
%g = alloca i32
%t1 = icmp eq i32* %b, null
@ -34,3 +35,28 @@ bb2: ; preds = %bb1, %bb
ret i32 %ret
}
define i8 @test2(i1 %cond, i32* %b, i32* %c) nounwind {
; CHECK: @test2
entry:
br i1 %cond, label %bb, label %bb1
bb:
%b1 = bitcast i32* %b to i8*
store i8 4, i8* %b1
br label %bb2
bb1:
%c1 = bitcast i32* %c to i8*
store i8 92, i8* %c1
br label %bb2
bb2:
%d = phi i32* [ %c, %bb1 ], [ %b, %bb ]
%d1 = bitcast i32* %d to i8*
%dv = load i8* %d1
; CHECK: %dv = phi i8
; CHECK-NOT: load
; CHECK: ret i8 %dv
ret i8 %dv
}