[X86, AVX] instcombine vperm2 intrinsics with zero inputs into shuffles
This is the IR optimizer follow-on patch for D8563: the x86 backend patch
that converts this kind of shuffle back into a vperm2.
This is also a continuation of the transform that started in D8486.
In that patch, Andrea suggested that we could convert vperm2 intrinsics that
use zero masks into a single shuffle.
This is an implementation of that suggestion.
Differential Revision: http://reviews.llvm.org/D8567
llvm-svn: 233110
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index b59c9f5..8f7825a 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -204,7 +204,7 @@
InstCombiner::BuilderTy &Builder) {
if (auto CInt = dyn_cast<ConstantInt>(II.getArgOperand(2))) {
VectorType *VecTy = cast<VectorType>(II.getType());
- uint8_t Imm = CInt->getZExtValue();
+ ConstantAggregateZero *ZeroVector = ConstantAggregateZero::get(VecTy);
// The immediate permute control byte looks like this:
// [1:0] - select 128 bits from sources for low half of destination
@@ -213,37 +213,51 @@
// [5:4] - select 128 bits from sources for high half of destination
// [6] - ignore
// [7] - zero high half of destination
+
+ uint8_t Imm = CInt->getZExtValue();
+
+ bool LowHalfZero = Imm & 0x08;
+ bool HighHalfZero = Imm & 0x80;
+
+ // If both zero mask bits are set, this was just a weird way to
+ // generate a zero vector.
+ if (LowHalfZero && HighHalfZero)
+ return ZeroVector;
+
+ // If 0 or 1 zero mask bits are set, this is a simple shuffle.
+ unsigned NumElts = VecTy->getNumElements();
+ unsigned HalfSize = NumElts / 2;
+ SmallVector<int, 8> ShuffleMask(NumElts);
+
+ // The high bit of the selection field chooses the 1st or 2nd operand.
+ bool LowInputSelect = Imm & 0x02;
+ bool HighInputSelect = Imm & 0x20;
- if ((Imm & 0x88) == 0x88) {
- // If both zero mask bits are set, this was just a weird way to
- // generate a zero vector.
- return ConstantAggregateZero::get(VecTy);
- }
+ // The low bit of the selection field chooses the low or high half
+ // of the selected operand.
+ bool LowHalfSelect = Imm & 0x01;
+ bool HighHalfSelect = Imm & 0x10;
- // TODO: If a single zero bit is set, replace one of the source operands
- // with a zero vector and use the same mask generation logic as below.
-
- if ((Imm & 0x88) == 0x00) {
- // If neither zero mask bit is set, this is a simple shuffle.
- unsigned NumElts = VecTy->getNumElements();
- unsigned HalfSize = NumElts / 2;
- unsigned HalfBegin;
- SmallVector<int, 8> ShuffleMask(NumElts);
-
- // Permute low half of result.
- HalfBegin = (Imm & 0x3) * HalfSize;
- for (unsigned i = 0; i != HalfSize; ++i)
- ShuffleMask[i] = HalfBegin + i;
+ // Determine which operand(s) are actually in use for this instruction.
+ Value *V0 = LowInputSelect ? II.getArgOperand(1) : II.getArgOperand(0);
+ Value *V1 = HighInputSelect ? II.getArgOperand(1) : II.getArgOperand(0);
- // Permute high half of result.
- HalfBegin = ((Imm >> 4) & 0x3) * HalfSize;
- for (unsigned i = HalfSize; i != NumElts; ++i)
- ShuffleMask[i] = HalfBegin + i - HalfSize;
+ // If needed, replace operands based on zero mask.
+ V0 = LowHalfZero ? ZeroVector : V0;
+ V1 = HighHalfZero ? ZeroVector : V1;
+
+ // Permute low half of result.
+ unsigned StartIndex = LowHalfSelect ? HalfSize : 0;
+ for (unsigned i = 0; i < HalfSize; ++i)
+ ShuffleMask[i] = StartIndex + i;
- Value *Op0 = II.getArgOperand(0);
- Value *Op1 = II.getArgOperand(1);
- return Builder.CreateShuffleVector(Op0, Op1, ShuffleMask);
- }
+ // Permute high half of result.
+ StartIndex = HighHalfSelect ? HalfSize : 0;
+ StartIndex += NumElts;
+ for (unsigned i = 0; i < HalfSize; ++i)
+ ShuffleMask[i + HalfSize] = StartIndex + i;
+
+ return Builder.CreateShuffleVector(V0, V1, ShuffleMask);
}
return nullptr;
}