[llvm] r374828 - [InstCombine] fold a shifted bool zext to a select
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Mon Oct 14 14:56:40 PDT 2019
Author: spatel
Date: Mon Oct 14 14:56:40 2019
New Revision: 374828
URL: http://llvm.org/viewvc/llvm-project?rev=374828&view=rev
Log:
[InstCombine] fold a shifted bool zext to a select
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
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp
llvm/trunk/test/Transforms/InstCombine/and.ll
llvm/trunk/test/Transforms/InstCombine/shift.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp?rev=374828&r1=374827&r2=374828&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineShifts.cpp Mon Oct 14 14:56:40 2019
@@ -934,6 +934,12 @@ Instruction *InstCombiner::visitShl(Bina
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;
}
Modified: llvm/trunk/test/Transforms/InstCombine/and.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/and.ll?rev=374828&r1=374827&r2=374828&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/and.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/and.ll Mon Oct 14 14:56:40 2019
@@ -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
Modified: llvm/trunk/test/Transforms/InstCombine/shift.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/shift.ll?rev=374828&r1=374827&r2=374828&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/shift.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/shift.ll Mon Oct 14 14:56:40 2019
@@ -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_spl
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>
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