[X86, SSE] instcombine common cases of insertps intrinsics into shuffles

[spatel]

Summary

This is very similar to D8486 (vperm2). If we treat insertps intrinsics as shufflevectors, we can optimize them better.

I've left all but the full zero case of the zero mask variants out of this patch. I don't think those can be converted into a single shuffle in all cases, but I'd be happy to be proven wrong as I was for vperm2f128.

Either way, we'd need to support whatever sequence we come up with for those cases in the backend before converting them here.

[majnemer]

lib/Transforms/InstCombine/InstCombineCalls.cpp

202

please make this auto *CInt so that it is more obvious that CInt is a pointer.

[spatel]

Patch updated:
Fixed the 'auto' to 'auto *' to make the pointer-ness explicit. Also fixed the line that I copy-pasted from. :)

[RKSimon]

This is looking pretty good. If the reason you haven't used the zmask more is to avoid the need for multiple shuffle stages is it worthwhile checking if the zmask (only) overrides the insertion destination, or cases where the 2 operands point to the same variable?

[spatel]

In D8833#151824, @RKSimon wrote:

This is looking pretty good. If the reason you haven't used the zmask more is to avoid the need for multiple shuffle stages is it worthwhile checking if the zmask (only) overrides the insertion destination, or cases where the 2 operands point to the same variable?

I thought about the case where the zmask overrides the insert, but I figured that was pretty far-fetched. I didn't consider the case where both inputs are the same. Let me know if you think those are worth chasing as stand-alone cases or if it's better to just solve the zmask case in general in the backend. Even if the oddball cases are worthy, I'd prefer to solve them in a follow-on patch just for the sake of patch minimalism.

[RKSimon]

In D8833#151845, @spatel wrote:

In D8833#151824, @RKSimon wrote:

This is looking pretty good. If the reason you haven't used the zmask more is to avoid the need for multiple shuffle stages is it worthwhile checking if the zmask (only) overrides the insertion destination, or cases where the 2 operands point to the same variable?

I thought about the case where the zmask overrides the insert, but I figured that was pretty far-fetched. I didn't consider the case where both inputs are the same. Let me know if you think those are worth chasing as stand-alone cases or if it's better to just solve the zmask case in general in the backend. Even if the oddball cases are worthy, I'd prefer to solve them in a follow-on patch just for the sake of patch minimalism.

I have ended up using both in downcoding, mainly due to register pressure problems:

• zeroing out lanes using insertps as we don't have a spare register for the xorps/blendps pattern
• reuse of the first operand - shuffle X00X

Its the second case that I think would be particular useful here but I'd be happy to see any improvements in a follow up patch.

[spatel]

Ping - can't tell if the last comment was an implicit 'LGTM'. :)

[RKSimon]

LGTM - getting those alternative shuffles (especially the X00X style) would be nice to have in any future patch but not necessary here.

[spatel]

Thanks, Simon - r235124.

I've put further insertps improvements on my list, so should have more patches in the near future.

lib/Transforms/InstCombine/InstCombineCalls.cpp

if (Len <= 8 && isPowerOf2_32((uint32_t)Len)) {
     // Set the size of the copy to 0, it will be deleted on the next iteration.
     MI->setLength(Constant::getNullValue(LenC->getType()));
     return MI;
   }
 
   return nullptr;
 }
 
+static Value *SimplifyX86insertps(const IntrinsicInst &II,
+                                  InstCombiner::BuilderTy &Builder) {
+  if (auto CInt = dyn_cast<ConstantInt>(II.getArgOperand(2))) {
+    VectorType *VecTy = cast<VectorType>(II.getType());
+    ConstantAggregateZero *ZeroVector = ConstantAggregateZero::get(VecTy);
+    
+    // The immediate permute control byte looks like this:
+    //    [3:0] - zero mask for each 32-bit lane
+    //    [5:4] - select one 32-bit destination lane
+    //    [7:6] - select one 32-bit source lane
+
+    uint8_t Imm = CInt->getZExtValue();
+    uint8_t ZMask = Imm & 0xf;
+    uint8_t DestLane = (Imm >> 4) & 0x3;
+    uint8_t SourceLane = (Imm >> 6) & 0x3;
+
+    // If all zero mask bits are set, this was just a weird way to
+    // generate a zero vector.
+    if (ZMask == 0xf)
+      return ZeroVector;
+    
+    // TODO: Model this case as two shuffles or a 'logical and' plus shuffle?
+    if (ZMask)
+      return nullptr;
+
+    assert(VecTy->getNumElements() == 4 && "insertps with wrong vector type");
+
+    // If we're not zeroing anything, this is a single shuffle.
+    // Replace the selected destination lane with the selected source lane.
+    // For all other lanes, pass the first source bits through.
+    int ShuffleMask[4] = { 0, 1, 2, 3 };
+    ShuffleMask[DestLane] = SourceLane + 4;
+    
+    return Builder.CreateShuffleVector(II.getArgOperand(0), II.getArgOperand(1),
+                                       ShuffleMask);
+  }
+  return nullptr;
+}
+
 /// The shuffle mask for a perm2*128 selects any two halves of two 256-bit
 /// source vectors, unless a zero bit is set. If a zero bit is set,
 /// then ignore that half of the mask and clear that half of the vector.
 static Value *SimplifyX86vperm2(const IntrinsicInst &II,
                                 InstCombiner::BuilderTy &Builder) {
   if (auto CInt = dyn_cast<ConstantInt>(II.getArgOperand(2))) {
     VectorType *VecTy = cast<VectorType>(II.getType());
     ConstantAggregateZero *ZeroVector = ConstantAggregateZero::get(VecTy);
case Intrinsic::x86_sse41_pmovzxdq: {
     APInt UndefElts(VWidth, 0);
     if (Value *TmpV = SimplifyDemandedVectorElts(
             II->getArgOperand(0), InputDemandedElts, UndefElts)) {
       II->setArgOperand(0, TmpV);
       return II;
     }
     break;
   }
+  case Intrinsic::x86_sse41_insertps:
+    if (Value *V = SimplifyX86insertps(*II, *Builder))
+      return ReplaceInstUsesWith(*II, V);
+    break;
     
   case Intrinsic::x86_sse4a_insertqi: {
     // insertqi x, y, 64, 0 can just copy y's lower bits and leave the top
     // ones undef
     // TODO: eventually we should lower this intrinsic to IR
     if (auto CIWidth = dyn_cast<ConstantInt>(II->getArgOperand(2))) {
       if (auto CIStart = dyn_cast<ConstantInt>(II->getArgOperand(3))) {
         unsigned Index = CIStart->getZExtValue();
         // From AMD documentation: "a value of zero in the field length is

test/Transforms/InstCombine/x86-insertps.ll

+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+declare <4 x float> @llvm.x86.sse41.insertps(<4 x float>, <4 x float>, i8) nounwind readnone
+
+; This should never happen, but make sure we don't crash handling a non-constant immediate byte.
+
+define <4 x float> @insertps_non_const_imm(<4 x float> %v1, <4 x float> %v2, i8 %c) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 %c)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_non_const_imm
+; CHECK-NEXT:  call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 %c)
+; CHECK-NEXT:  ret <4 x float>
+}
+
+; If all zero mask bits are set, return a zero regardless of the other control bits.
+
+define <4 x float> @insertps_0x0f(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 15)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0x0f
+; CHECK-NEXT:  ret <4 x float> zeroinitializer
+}
+define <4 x float> @insertps_0xff(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 255)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0xff
+; CHECK-NEXT:  ret <4 x float> zeroinitializer
+}
+
+; If some zero mask bits are set, we do not change anything.
+
+define <4 x float> @insertps_0x03(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 3)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0x03
+; CHECK-NEXT:  call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 3)
+; CHECK-NEXT:  ret <4 x float>
+}
+
+; If no zero mask bits are set, convert to a shuffle.
+
+define <4 x float> @insertps_0x00(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 0)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0x00
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 4, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0x10(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 16)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0x10
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 0, i32 4, i32 2, i32 3>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0x20(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 32)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0x20
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 0, i32 1, i32 4, i32 3>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0x30(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 48)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0x30
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 0, i32 1, i32 2, i32 4>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0xc0(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 192)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0xc0
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 7, i32 1, i32 2, i32 3>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0xd0(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 208)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0xd0
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 0, i32 7, i32 2, i32 3>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0xe0(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 224)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0xe0
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 0, i32 1, i32 7, i32 3>
+; CHECK-NEXT:  ret <4 x float>
+}
+
+define <4 x float> @insertps_0xf0(<4 x float> %v1, <4 x float> %v2) {
+  %res = call <4 x float> @llvm.x86.sse41.insertps(<4 x float> %v1, <4 x float> %v2, i8 240)
+  ret <4 x float> %res
+
+; CHECK-LABEL: @insertps_0xf0
+; CHECK-NEXT:  shufflevector <4 x float> %v1, <4 x float> %v2, <4 x i32> <i32 0, i32 1, i32 2, i32 7>
+; CHECK-NEXT:  ret <4 x float>
+}
+