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[InstCombine] X - 0 is equal to X, not undef

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A refactoring made @llvm.ssub.with.overflow.i32(i32 %X, i32 0) transform
into undef instead of %X.

This fixes PR23624.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237968 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2015-05-21 23:04:21 +00:00
parent 1052042adf
commit 41af60bdc0
2 changed files with 28 additions and 26 deletions
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46
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -2141,13 +2141,11 @@ bool InstCombiner::OptimizeOverflowCheck(OverflowCheckFlavor OCF, Value *LHS,
case OCF_SIGNED_ADD: {
// X + undef -> undef
if (isa<UndefValue>(RHS))
return SetResult(UndefValue::get(RHS->getType()),
UndefValue::get(Builder->getInt1Ty()), false);
return SetResult(RHS, UndefValue::get(Builder->getInt1Ty()), false);
if (ConstantInt *ConstRHS = dyn_cast<ConstantInt>(RHS))
// X + 0 -> {X, false}
if (ConstRHS->isZero())
return SetResult(LHS, Builder->getFalse(), false);
// X + 0 -> {X, false}
if (match(RHS, m_Zero()))
return SetResult(LHS, Builder->getFalse(), false);
// We can strength reduce this signed add into a regular add if we can prove
// that it will never overflow.
@ -2160,16 +2158,16 @@ bool InstCombiner::OptimizeOverflowCheck(OverflowCheckFlavor OCF, Value *LHS,
case OCF_UNSIGNED_SUB:
case OCF_SIGNED_SUB: {
// undef - X -> undef
// X - undef -> undef
if (isa<UndefValue>(LHS) || isa<UndefValue>(RHS))
return SetResult(UndefValue::get(LHS->getType()),
UndefValue::get(Builder->getInt1Ty()), false);
if (isa<UndefValue>(LHS))
return SetResult(LHS, UndefValue::get(Builder->getInt1Ty()), false);
if (ConstantInt *ConstRHS = dyn_cast<ConstantInt>(RHS))
// X - 0 -> {X, false}
if (ConstRHS->isZero())
return SetResult(UndefValue::get(LHS->getType()), Builder->getFalse(),
false);
// X - undef -> undef
if (isa<UndefValue>(RHS))
return SetResult(RHS, UndefValue::get(Builder->getInt1Ty()), false);
// X - 0 -> {X, false}
if (match(RHS, m_Zero()))
return SetResult(LHS, Builder->getFalse(), false);
if (OCF == OCF_SIGNED_SUB) {
if (WillNotOverflowSignedSub(LHS, RHS, OrigI))
@ -2194,19 +2192,15 @@ bool InstCombiner::OptimizeOverflowCheck(OverflowCheckFlavor OCF, Value *LHS,
case OCF_SIGNED_MUL:
// X * undef -> undef
if (isa<UndefValue>(RHS))
return SetResult(UndefValue::get(LHS->getType()),
UndefValue::get(Builder->getInt1Ty()), false);
return SetResult(RHS, UndefValue::get(Builder->getInt1Ty()), false);
if (ConstantInt *RHSI = dyn_cast<ConstantInt>(RHS)) {
// X * 0 -> {0, false}
if (RHSI->isZero())
return SetResult(Constant::getNullValue(RHS->getType()),
Builder->getFalse(), false);
// X * 0 -> {0, false}
if (match(RHS, m_Zero()))
return SetResult(RHS, Builder->getFalse(), false);
// X * 1 -> {X, false}
if (RHSI->equalsInt(1))
return SetResult(LHS, Builder->getFalse(), false);
}
// X * 1 -> {X, false}
if (match(RHS, m_One()))
return SetResult(LHS, Builder->getFalse(), false);
if (OCF == OCF_SIGNED_MUL)
if (WillNotOverflowSignedMul(LHS, RHS, OrigI))

8
test/Transforms/InstCombine/intrinsics.ll
View File

@ -417,3 +417,11 @@ define %ov.result.32 @ssubtest_reorder(i8 %a) {
; CHECK-NEXT: %1 = insertvalue %ov.result.32 { i32 undef, i1 false }, i32 %x, 0
; CHECK-NEXT: ret %ov.result.32 %1
}
define %ov.result.32 @never_overflows_ssub(i32 %a) {
%x = call %ov.result.32 @llvm.ssub.with.overflow.i32(i32 %a, i32 0)
ret %ov.result.32 %x
; CHECK-LABEL: @never_overflows_ssub
; CHECK-NEXT: %[[x:.*]] = insertvalue %ov.result.32 { i32 undef, i1 false }, i32 %a, 0
; CHECK-NEXT: ret %ov.result.32 %[[x]]
}