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[InstCombine] remove one-use restriction for icmp (shr exact X, C1), C2 --> icmp X, (C2<<C1) 

llvm-svn: 314698
This commit is contained in:
Sanjay Patel 2017-10-02 18:26:44 +00:00
parent acdf91817e
commit 6e17c00a88
2 changed files with 7 additions and 7 deletions
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12
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -2058,15 +2058,15 @@ Instruction *InstCombiner::foldICmpShrConstant(ICmpInst &Cmp,
(!IsAShr && C->shl(ShAmtVal).lshr(ShAmtVal) == *C)) &&
"Expected icmp+shr simplify did not occur.");
// Check if the bits shifted out are known to be zero. If so, we can compare
// against the unshifted value:
// If the bits shifted out are known zero, compare the unshifted value:
// (X & 4) >> 1 == 2 --> (X & 4) == 4.
Constant *ShiftedCmpRHS = ConstantInt::get(Shr->getType(), *C << ShAmtVal);
if (Shr->hasOneUse()) {
if (Shr->isExact())
return new ICmpInst(Pred, X, ShiftedCmpRHS);
if (Shr->isExact())
return new ICmpInst(Pred, X, ShiftedCmpRHS);
// Otherwise strength reduce the shift into an 'and'.
if (Shr->hasOneUse()) {
// Canonicalize the shift into an 'and':
// icmp eq/ne (shr X, ShAmt), C --> icmp eq/ne (and X, HiMask), (C << ShAmt)
APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal));
Constant *Mask = ConstantInt::get(Shr->getType(), Val);
Value *And = Builder.CreateAnd(X, Mask, Shr->getName() + ".mask");

2
llvm/test/Transforms/InstCombine/icmp-shr.ll
View File

@ -483,7 +483,7 @@ declare void @foo(i32)
define i1 @exact_multiuse(i32 %x) {
; CHECK-LABEL: @exact_multiuse(
; CHECK-NEXT: [[SH:%.*]] = lshr exact i32 %x, 7
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[SH]], 1024
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 %x, 131072
; CHECK-NEXT: call void @foo(i32 [[SH]])
; CHECK-NEXT: ret i1 [[CMP]]
;