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[InstCombine] bitrev (zext i1 X) --> select X, SMinC, 0

Browse Source 
https://alive2.llvm.org/ce/z/ZXCtgi

This breaks the infinite combine loop for issue #59897,
but we may still need more changes to avoid those loops.
This commit is contained in:
Sanjay Patel
2023-01-09 12:25:02 -05:00
parent b1e6947618
commit 0eedc9e567
2 changed files with 30 additions and 3 deletions
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12
llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
View File

@@ -1441,6 +1441,18 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
break;
}
case Intrinsic::bitreverse: {
// bitrev (zext i1 X to ?) --> X ? SignBitC : 0
Value *X;
if (match(II->getArgOperand(0), m_ZExt(m_Value(X))) &&
X->getType()->isIntOrIntVectorTy(1)) {
Type *Ty = II->getType();
APInt SignBit = APInt::getSignMask(Ty->getScalarSizeInBits());
return SelectInst::Create(X, ConstantInt::get(Ty, SignBit),
ConstantInt::getNullValue(Ty));
}
break;
}
case Intrinsic::bswap: {
Value *IIOperand = II->getArgOperand(0);

21
llvm/test/Transforms/InstCombine/bitreverse.ll
View File

@@ -323,7 +323,7 @@ define i32 @rev_i1(i1 %x) {
; CHECK-LABEL: @rev_i1(
; CHECK-NEXT: [[Z:%.*]] = zext i1 [[X:%.*]] to i32
; CHECK-NEXT: call void @use_i32(i32 [[Z]])
; CHECK-NEXT: [[R:%.*]] = call i32 @llvm.bitreverse.i32(i32 [[Z]])
; CHECK-NEXT: [[R:%.*]] = select i1 [[X]], i32 -2147483648, i32 0
; CHECK-NEXT: ret i32 [[R]]
;
%z = zext i1 %x to i32
@@ -334,8 +334,7 @@ define i32 @rev_i1(i1 %x) {
define <2 x i8> @rev_v2i1(<2 x i1> %x) {
; CHECK-LABEL: @rev_v2i1(
; CHECK-NEXT: [[Z:%.*]] = zext <2 x i1> [[X:%.*]] to <2 x i8>
; CHECK-NEXT: [[R:%.*]] = call <2 x i8> @llvm.bitreverse.v2i8(<2 x i8> [[Z]])
; CHECK-NEXT: [[R:%.*]] = select <2 x i1> [[X:%.*]], <2 x i8> <i8 -128, i8 -128>, <2 x i8> zeroinitializer
; CHECK-NEXT: ret <2 x i8> [[R]]
;
%z = zext <2 x i1> %x to <2 x i8>
@@ -353,3 +352,19 @@ define i32 @rev_i2(i2 %x) {
%r = call i32 @llvm.bitreverse.i32(i32 %z)
ret i32 %r
}
; This used to infinite loop.
define i64 @PR59897(i1 %X1_2) {
; CHECK-LABEL: @PR59897(
; CHECK-NEXT: [[NOT_X1_2:%.*]] = xor i1 [[X1_2:%.*]], true
; CHECK-NEXT: [[X0_3X2X5X0:%.*]] = zext i1 [[NOT_X1_2]] to i64
; CHECK-NEXT: ret i64 [[X0_3X2X5X0]]
;
%X1_3 = zext i1 %X1_2 to i32
%X8_3x2x2x0 = call i32 @llvm.bitreverse.i32(i32 %X1_3)
%X8_4x2x3x0 = xor i32 %X8_3x2x2x0, -1
%X0_3x2x4x0 = lshr i32 %X8_4x2x3x0, 31
%X0_3x2x5x0 = zext i32 %X0_3x2x4x0 to i64
ret i64 %X0_3x2x5x0
}