[PATCH] D63382: [InstCombine] fold a shifted zext to a select

[Sanjay Patel via Phabricator via llvm-commits]

spatel updated this revision to Diff 224904.
spatel added a comment.

Patch updated:
Rebased after committing baseline tests and cosmetic changes to the code.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D63382/new/

https://reviews.llvm.org/D63382

Files:
  llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
  llvm/test/Transforms/InstCombine/and.ll
  llvm/test/Transforms/InstCombine/shift.ll


Index: llvm/test/Transforms/InstCombine/shift.ll
===================================================================
--- llvm/test/Transforms/InstCombine/shift.ll
+++ llvm/test/Transforms/InstCombine/shift.ll
@@ -1181,8 +1181,7 @@
 
 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 <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_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>
Index: llvm/test/Transforms/InstCombine/and.ll
===================================================================
--- llvm/test/Transforms/InstCombine/and.ll
+++ llvm/test/Transforms/InstCombine/and.ll
@@ -346,8 +346,7 @@
 
 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
Index: llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -934,6 +934,12 @@
     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;
 }
 


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