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

[Zvi Rackover via Phabricator via llvm-commits]

zvi updated this revision to Diff 204955.
zvi added a comment.

Fix typo in comment pointed out by @xbolva00


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
@@ -1191,6 +1191,36 @@
   ret i64 %shl
 }
 
+define i32 @test_shl_zext_bool(i1 %t) {
+; CHECK-LABEL: @test_shl_zext_bool(
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 %t, i32 4, i32 0
+; CHECK-NEXT:    ret i32 [[SEL]]
+;
+  %ext = zext i1 %t to i32
+  %shl = shl i32 %ext, 2
+  ret i32 %shl
+}
+
+define <2 x i32> @test_shl_zext_bool_splat(<2 x i1> %t) {
+; CHECK-LABEL: @test_shl_zext_bool_splat(
+; CHECK-NEXT:    [[SEL:%.*]] = select <2 x i1> %t, <2 x i32> <i32 8, i32 8>, <2 x i32> zeroinitializer
+; CHECK-NEXT:    ret <2 x i32> [[SEL]]
+;
+  %ext = zext <2 x i1> %t to <2 x i32>
+  %shl = shl <2 x i32> %ext, <i32 3, i32 3>
+  ret <2 x i32> %shl
+}
+
+define <2 x i32> @test_shl_zext_bool_vec(<2 x i1> %t) {
+; CHECK-LABEL: @test_shl_zext_bool_vec(
+; CHECK-NEXT:    [[SEL:%.*]] = select <2 x i1> %t, <2 x i32> <i32 4, i32 8>, <2 x i32> zeroinitializer
+; CHECK-NEXT:    ret <2 x i32> [[SEL]]
+;
+  %ext = zext <2 x i1> %t to <2 x i32>
+  %shl = shl <2 x i32> %ext, <i32 2, i32 3>
+  ret <2 x i32> %shl
+}
+
 define <2 x i64> @test_64_splat_vec(<2 x i32> %t) {
 ; CHECK-LABEL: @test_64_splat_vec(
 ; CHECK-NEXT:    [[TMP1:%.*]] = shl <2 x i32> %t, <i32 8, i32 8>
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
@@ -582,10 +582,10 @@
 
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
   Type *Ty = I.getType();
+  unsigned BitWidth = Ty->getScalarSizeInBits();
   const APInt *ShAmtAPInt;
   if (match(Op1, m_APInt(ShAmtAPInt))) {
     unsigned ShAmt = ShAmtAPInt->getZExtValue();
-    unsigned BitWidth = Ty->getScalarSizeInBits();
 
     // shl (zext X), ShAmt --> zext (shl X, ShAmt)
     // This is only valid if X would have zeros shifted out.
@@ -668,6 +668,13 @@
     // (X * C2) << C1 --> X * (C2 << C1)
     if (match(Op0, m_Mul(m_Value(X), m_Constant(C2))))
       return BinaryOperator::CreateMul(X, ConstantExpr::getShl(C2, C1));
+
+    // shl (zext (i1 X)), C1 --> select (X, 1 << C1, 0)
+    if (match(Op0, m_ZExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1)) {
+      return SelectInst::Create(
+          X, ConstantExpr::getShl(ConstantInt::get(Ty, APInt(BitWidth, 1)), C1),
+          ConstantInt::get(Ty, 0));
+    }
   }
 
   return nullptr;


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