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Revert remaining part of r93200: "Disable folding sext(trunc(x)) -> x"

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This fixes PR5997.

These transforms were disabled because codegen couldn't deal with other
uses of trunc(x). This is now handled by the peephole pass.

This causes no regressions on x86-64.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159003 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen 2012-06-22 16:36:43 +00:00
parent 63e0e8d90b
commit 7ee3ca10f5
2 changed files with 11 additions and 15 deletions
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13
lib/Transforms/InstCombine/InstCombineCasts.cpp
View File

@ -648,10 +648,8 @@ static bool CanEvaluateZExtd(Value *V, Type *Ty, unsigned &BitsToClear) {
if (!I) return false;
// If the input is a truncate from the destination type, we can trivially
// eliminate it, even if it has multiple uses.
// FIXME: This is currently disabled until codegen can handle this without
// pessimizing code, PR5997.
if (0 && isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
// eliminate it.
if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
return true;
// We can't extend or shrink something that has multiple uses: doing so would
@ -992,11 +990,8 @@ static bool CanEvaluateSExtd(Value *V, Type *Ty) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return false;
// If this is a truncate from the dest type, we can trivially eliminate it,
// even if it has multiple uses.
// FIXME: This is currently disabled until codegen can handle this without
// pessimizing code, PR5997.
if (0 && isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
// If this is a truncate from the dest type, we can trivially eliminate it.
if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
return true;
// We can't extend or shrink something that has multiple uses: doing so would

13
test/Transforms/InstCombine/trunc.ll
View File

@ -12,8 +12,8 @@ define i64 @test1(i64 %a) {
call void @use(i32 %b)
ret i64 %d
; CHECK: @test1
; CHECK: %d = and i64 %a, 15
; CHECK: ret i64 %d
; CHECK-NOT: ext
; CHECK: ret
}
define i64 @test2(i64 %a) {
%b = trunc i64 %a to i32
@ -34,8 +34,8 @@ define i64 @test3(i64 %a) {
call void @use(i32 %b)
ret i64 %d
; CHECK: @test3
; CHECK: %d = and i64 %a, 8
; CHECK: ret i64 %d
; CHECK-NOT: ext
; CHECK: ret
}
define i64 @test4(i64 %a) {
%b = trunc i64 %a to i32
@ -46,8 +46,9 @@ define i64 @test4(i64 %a) {
ret i64 %d
; CHECK: @test4
; CHECK: = and i64 %a, 8
; CHECK: %d = xor i64 {{.*}}, 8
; CHECK: ret i64 %d
; CHECK: = xor i64 {{.*}}, 8
; CHECK-NOT: ext
; CHECK: ret
}
define i32 @test5(i32 %A) {