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[InstCombine] fold a shifted bool zext to a select

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For a constant shift amount, add the following fold.
shl (zext (i1 X)), ShAmt --> select (X, 1 << ShAmt, 0)

https://rise4fun.com/Alive/IZ9

Fixes PR42257.

Based on original patch by @zvi (Zvi Rackover)

Differential Revision: https://reviews.llvm.org/D63382

llvm-svn: 374828
This commit is contained in:
Sanjay Patel 2019-10-14 21:56:40 +00:00
parent 9585d8c11a
commit 1f40f15d54
3 changed files with 10 additions and 8 deletions
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6
llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
View File

@ -934,6 +934,12 @@ Instruction *InstCombiner::visitShl(BinaryOperator &I) {
return BinaryOperator::CreateLShr(
ConstantInt::get(Ty, APInt::getSignMask(BitWidth)), X);
// shl (zext (i1 X)), C1 --> select (X, 1 << C1, 0)
if (match(Op0, m_ZExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1)) {
auto *NewC = ConstantExpr::getShl(ConstantInt::get(Ty, 1), C1);
return SelectInst::Create(X, NewC, ConstantInt::getNullValue(Ty));
}
return nullptr;
}

3
llvm/test/Transforms/InstCombine/and.ll
View File

@ -346,8 +346,7 @@ define i32 @test30(i1 %X) {
define i32 @test31(i1 %X) {
; CHECK-LABEL: @test31(
; CHECK-NEXT: [[Y:%.*]] = zext i1 %X to i32
; CHECK-NEXT: [[Z:%.*]] = shl nuw nsw i32 [[Y]], 4
; CHECK-NEXT: [[Z:%.*]] = select i1 [[X:%.*]], i32 16, i32 0
; CHECK-NEXT: ret i32 [[Z]]
;
%Y = zext i1 %X to i32

9
llvm/test/Transforms/InstCombine/shift.ll
View File

@ -1181,8 +1181,7 @@ define <2 x i65> @test_63(<2 x i64> %t) {
define i32 @test_shl_zext_bool(i1 %t) {
; CHECK-LABEL: @test_shl_zext_bool(
; CHECK-NEXT: [[EXT:%.*]] = zext i1 [[T:%.*]] to i32
; CHECK-NEXT: [[SHL:%.*]] = shl nuw nsw i32 [[EXT]], 2
; CHECK-NEXT: [[SHL:%.*]] = select i1 [[T:%.*]], i32 4, i32 0
; CHECK-NEXT: ret i32 [[SHL]]
;
%ext = zext i1 %t to i32
@ -1192,8 +1191,7 @@ define i32 @test_shl_zext_bool(i1 %t) {
define <2 x i32> @test_shl_zext_bool_splat(<2 x i1> %t) {
; CHECK-LABEL: @test_shl_zext_bool_splat(
; CHECK-NEXT: [[EXT:%.*]] = zext <2 x i1> [[T:%.*]] to <2 x i32>
; CHECK-NEXT: [[SHL:%.*]] = shl nuw nsw <2 x i32> [[EXT]], <i32 3, i32 3>
; CHECK-NEXT: [[SHL:%.*]] = select <2 x i1> [[T:%.*]], <2 x i32> <i32 8, i32 8>, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[SHL]]
;
%ext = zext <2 x i1> %t to <2 x i32>
@ -1203,8 +1201,7 @@ define <2 x i32> @test_shl_zext_bool_splat(<2 x i1> %t) {
define <2 x i32> @test_shl_zext_bool_vec(<2 x i1> %t) {
; CHECK-LABEL: @test_shl_zext_bool_vec(
; CHECK-NEXT: [[EXT:%.*]] = zext <2 x i1> [[T:%.*]] to <2 x i32>
; CHECK-NEXT: [[SHL:%.*]] = shl <2 x i32> [[EXT]], <i32 2, i32 3>
; CHECK-NEXT: [[SHL:%.*]] = select <2 x i1> [[T:%.*]], <2 x i32> <i32 4, i32 8>, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i32> [[SHL]]
;
%ext = zext <2 x i1> %t to <2 x i32>