From 466e0f38d344fd1a64b7be2b3c4e3f7003ef4fef Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Thu, 27 Sep 2012 08:33:56 +0000
Subject: Prefer shuffles to selects. Backends love shuffles!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164763 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/InstCombine/InstCombineSelect.cpp | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

(limited to 'lib/Transforms/InstCombine/InstCombineSelect.cpp')

diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 291e80019e..70483ceb06 100644
--- a/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -903,7 +903,7 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
     return &SI;
   }
 
-  if (VectorType* VecTy = dyn_cast<VectorType>(SI.getType())) {
+  if (VectorType *VecTy = dyn_cast<VectorType>(SI.getType())) {
     unsigned VWidth = VecTy->getNumElements();
     APInt UndefElts(VWidth, 0);
     APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
@@ -912,6 +912,24 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
         return ReplaceInstUsesWith(SI, V);
       return &SI;
     }
+
+    if (ConstantVector *CV = dyn_cast<ConstantVector>(CondVal)) {
+      // Form a shufflevector instruction.
+      SmallVector<Constant *, 8> Mask(VWidth);
+      Type *Int32Ty = Type::getInt32Ty(CV->getContext());
+      for (unsigned i = 0; i != VWidth; ++i) {
+        Constant *Elem = cast<Constant>(CV->getOperand(i));
+        if (ConstantInt *E = dyn_cast<ConstantInt>(Elem))
+          Mask[i] = ConstantInt::get(Int32Ty, i + (E->isZero() ? VWidth : 0));
+        else if (isa<UndefValue>(Elem))
+          Mask[i] = UndefValue::get(Int32Ty);
+        else
+          return 0;
+      }
+      Constant *MaskVal = ConstantVector::get(Mask);
+      Value *V = Builder->CreateShuffleVector(TrueVal, FalseVal, MaskVal);
+      return ReplaceInstUsesWith(SI, V);
+    }
   }
 
   return 0;
-- 
cgit v1.2.3-70-g09d2


From 7e0e166d1783671e555eff26b9932012fadea691 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Fri, 28 Sep 2012 09:33:53 +0000
Subject: Surprisingly, we missed a trivial case here. Fix that!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164814 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/InstCombine/InstCombineSelect.cpp | 4 ++++
 test/Transforms/InstCombine/vec_shuffle.ll       | 8 ++++++++
 2 files changed, 12 insertions(+)

(limited to 'lib/Transforms/InstCombine/InstCombineSelect.cpp')

diff --git a/lib/Transforms/InstCombine/InstCombineSelect.cpp b/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 70483ceb06..0ba7340e64 100644
--- a/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -930,6 +930,10 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
       Value *V = Builder->CreateShuffleVector(TrueVal, FalseVal, MaskVal);
       return ReplaceInstUsesWith(SI, V);
     }
+
+    if (isa<ConstantAggregateZero>(CondVal)) {
+      return ReplaceInstUsesWith(SI, FalseVal);
+    }
   }
 
   return 0;
diff --git a/test/Transforms/InstCombine/vec_shuffle.ll b/test/Transforms/InstCombine/vec_shuffle.ll
index a7f9fcfbe0..14f532195d 100644
--- a/test/Transforms/InstCombine/vec_shuffle.ll
+++ b/test/Transforms/InstCombine/vec_shuffle.ll
@@ -188,3 +188,11 @@ define <4 x i16> @test13d(<4 x i16> %lhs, <4 x i16> %rhs) {
            <4 x i16> %lhs, <4 x i16> %rhs
   ret <4 x i16> %A
 }
+
+define <4 x i16> @test13e(<4 x i16> %lhs, <4 x i16> %rhs) {
+; CHECK: @test13e
+; CHECK-NEXT: ret <4 x i16> %rhs
+  %A = select <4 x i1> <i1 false, i1 false, i1 false, i1 false>,
+           <4 x i16> %lhs, <4 x i16> %rhs
+  ret <4 x i16> %A
+}
-- 
cgit v1.2.3-70-g09d2