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

[Zvi Rackover via Phabricator via llvm-commits]

zvi updated this revision to Diff 204943.
zvi added a comment.

Addressed comments by @lebedev.ri 
Thanks!


Repository:
  rG LLVM Github Monorepo

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 +1191,26 @@
   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 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
@@ -587,14 +587,21 @@
     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.
     Value *X;
     if (match(Op0, m_ZExt(m_Value(X)))) {
       unsigned SrcWidth = X->getType()->getScalarSizeInBits();
+      // shl (zext X), ShAmt --> zext (shl X, ShAmt)
+      // This is only valid if X would have zeros shifted out.
       if (ShAmt < SrcWidth &&
           MaskedValueIsZero(X, APInt::getHighBitsSet(SrcWidth, ShAmt), 0, &I))
         return new ZExtInst(Builder.CreateShl(X, ShAmt), Ty);
+
+      // shl (zext (i1 X)), ShAmt --> select (X, 0, 1 << ShAmt)
+      if (X->getType()->isIntOrIntVectorTy(1)) {
+        return SelectInst::Create(
+            X, ConstantInt::get(Ty, APInt(BitWidth, 1) << ShAmt),
+            ConstantInt::get(Ty, 0));
+      }
     }
 
     // (X >> C) << C --> X & (-1 << C)


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D63382.204943.patch
Type: text/x-patch
Size: 2735 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190616/cfacaacf/attachment.bin>