[InstCombine] Move SSE2/AVX2 arithmetic vector shift folding to instcombiner

As discussed in D11760, this patch moves the (V)PSRA(WD) arithmetic shift-by-constant folding to InstCombine to match the logical shift implementations.

Differential Revision: http://reviews.llvm.org/D11886

llvm-svn: 244495

1 files changed, 31 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index de413c42348..600c8c36392 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -199,7 +199,9 @@ Instruction *InstCombiner::SimplifyMemSet(MemSetInst *MI) {
 
 static Value *SimplifyX86immshift(const IntrinsicInst &II,
                                   InstCombiner::BuilderTy &Builder,
-                                  bool ShiftLeft) {
+                                  bool LogicalShift, bool ShiftLeft) {
+  assert((LogicalShift || !ShiftLeft) && "Only logical shifts can shift left");
+
   // Simplify if count is constant.
   auto Arg1 = II.getArgOperand(1);
   auto CAZ = dyn_cast<ConstantAggregateZero>(Arg1);
@@ -238,9 +240,15 @@ static Value *SimplifyX86immshift(const IntrinsicInst &II,
   if (Count == 0)
     return Vec;
 
-  // Handle cases when Shift >= BitWidth - just return zero.
-  if (Count.uge(BitWidth))
-    return ConstantAggregateZero::get(VT);
+  // Handle cases when Shift >= BitWidth.
+  if (Count.uge(BitWidth)) {
+    // If LogicalShift - just return zero.
+    if (LogicalShift)
+      return ConstantAggregateZero::get(VT);
+
+    // If ArithmeticShift - clamp Shift to (BitWidth - 1).
+    Count = APInt(64, BitWidth - 1);
+  }
 
   // Get a constant vector of the same type as the first operand.
   auto ShiftAmt = ConstantInt::get(SVT, Count.zextOrTrunc(BitWidth));
@@ -249,7 +257,10 @@ static Value *SimplifyX86immshift(const IntrinsicInst &II,
   if (ShiftLeft)
     return Builder.CreateShl(Vec, ShiftVec);
 
-  return Builder.CreateLShr(Vec, ShiftVec);
+  if (LogicalShift)
+    return Builder.CreateLShr(Vec, ShiftVec);
+
+  return Builder.CreateAShr(Vec, ShiftVec);
 }
 
 static Value *SimplifyX86extend(const IntrinsicInst &II,
@@ -776,6 +787,19 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
     break;
   }
 
+  // Constant fold ashr( <A x Bi>, Ci ).
+  case Intrinsic::x86_sse2_psra_d:
+  case Intrinsic::x86_sse2_psra_w:
+  case Intrinsic::x86_sse2_psrai_d:
+  case Intrinsic::x86_sse2_psrai_w:
+  case Intrinsic::x86_avx2_psra_d:
+  case Intrinsic::x86_avx2_psra_w:
+  case Intrinsic::x86_avx2_psrai_d:
+  case Intrinsic::x86_avx2_psrai_w:
+    if (Value *V = SimplifyX86immshift(*II, *Builder, false, false))
+      return ReplaceInstUsesWith(*II, V);
+    break;
+
   // Constant fold lshr( <A x Bi>, Ci ).
   case Intrinsic::x86_sse2_psrl_d:
   case Intrinsic::x86_sse2_psrl_q:
@@ -789,7 +813,7 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
   case Intrinsic::x86_avx2_psrli_d:
   case Intrinsic::x86_avx2_psrli_q:
   case Intrinsic::x86_avx2_psrli_w:
-    if (Value *V = SimplifyX86immshift(*II, *Builder, false))
+    if (Value *V = SimplifyX86immshift(*II, *Builder, true, false))
       return ReplaceInstUsesWith(*II, V);
     break;
 
@@ -806,7 +830,7 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
   case Intrinsic::x86_avx2_pslli_d:
   case Intrinsic::x86_avx2_pslli_q:
   case Intrinsic::x86_avx2_pslli_w:
-    if (Value *V = SimplifyX86immshift(*II, *Builder, true))
+    if (Value *V = SimplifyX86immshift(*II, *Builder, true, true))
       return ReplaceInstUsesWith(*II, V);
     break;