[TargetLowering] Add SimplifyDemandedBits support for ISD::INSERT_VECTOR_ELT

[RKSimon]

Summary

This helps us relax the extension of a lot of scalar elements before they are inserted into a vector.

Its exposes an issue in DAGCombiner::convertBuildVecZextToZext as some/all the zero-extensions may be relaxed to ANY_EXTEND, so we need to handle that case to avoid a couple of AVX2 VPMOVZX test regressions.

Once this is in it should be easier to fix a number of remaining failures to fold loads into VBROADCAST nodes.

[RKSimon]

ping?

[nikic]

lib/CodeGen/SelectionDAG/TargetLowering.cpp

578

Why is this check necessary? If there are no demanded elements, wouldn't this allow folding the input vector to undef?

[RKSimon]

Always call SimplifyDemandedBits on the base vector to force to UNDEF - I wasn't doing this beforehand to try and avoid losing KnownBits info but we can just ignore the KnownBits from the base vector if its not actually demanded.

[nikic]

LGTM

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

for (unsigned In = 0, Len = CurSize / 2; In < Len; ++In) {
           DAG.getVectorShuffle(VT, DL, Shuffles[Left], Shuffles[Right], Mask);
     }
   }
   return Shuffles[0];
 }
 
 // Try to turn a build vector of zero extends of extract vector elts into a
 // a vector zero extend and possibly an extract subvector.
-// TODO: Support sign extend or any extend?
+// TODO: Support sign extend?
 // TODO: Allow undef elements?
-// TODO: Don't require the extracts to start at element 0.
 SDValue DAGCombiner::convertBuildVecZextToZext(SDNode *N) {
   if (LegalOperations)
     return SDValue();
 
   EVT VT = N->getValueType(0);
 
+  bool FoundZeroExtend = false;
   SDValue Op0 = N->getOperand(0);
   auto checkElem = [&](SDValue Op) -> int64_t {
-    if (Op.getOpcode() == ISD::ZERO_EXTEND &&
+    unsigned Opc = Op.getOpcode();
+    FoundZeroExtend |= (Opc == ISD::ZERO_EXTEND);
+    if ((Opc == ISD::ZERO_EXTEND || Opc == ISD::ANY_EXTEND) &&
         Op.getOperand(0).getOpcode() == ISD::EXTRACT_VECTOR_ELT &&
         Op0.getOperand(0).getOperand(0) == Op.getOperand(0).getOperand(0))
       if (auto *C = dyn_cast<ConstantSDNode>(Op.getOperand(0).getOperand(1)))
         return C->getZExtValue();
     return -1;
   };
 
   // Make sure the first element matches
SDValue DAGCombiner::convertBuildVecZextToZext(SDNode *N) {
   for (unsigned i = 1; i != NumElems; ++i) {
     if ((Offset + i) != checkElem(N->getOperand(i)))
       return SDValue();
   }
 
   SDLoc DL(N);
   In = DAG.getNode(ISD::EXTRACT_SUBVECTOR, DL, InVT, In,
                    Op0.getOperand(0).getOperand(1));
-  return DAG.getNode(ISD::ZERO_EXTEND, DL, VT, In);
+  return DAG.getNode(FoundZeroExtend ? ISD::ZERO_EXTEND : ISD::ANY_EXTEND, DL,
+                     VT, In);
 }
 
 SDValue DAGCombiner::visitBUILD_VECTOR(SDNode *N) {
   EVT VT = N->getValueType(0);
 
   // A vector built entirely of undefs is undef.
   if (ISD::allOperandsUndef(N))
     return DAG.getUNDEF(VT);

lib/CodeGen/SelectionDAG/TargetLowering.cpp

for (SDValue SrcOp : Op->ops()) {
       }
 
       // Known bits are the values that are shared by every element.
       // TODO: support per-element known bits.
       Known.One &= Known2.One;
       Known.Zero &= Known2.Zero;
     }
     return false; // Don't fall through, will infinitely loop.
+  case ISD::INSERT_VECTOR_ELT: {
+    SDValue Vec = Op.getOperand(0);
+    SDValue Scl = Op.getOperand(1);
+    auto *CIdx = dyn_cast<ConstantSDNode>(Op.getOperand(2));
+    EVT VecVT = Vec.getValueType();
+
+    // If index isn't constant, assume we need all vector elements AND the
+    // inserted element.
+    APInt DemandedVecElts(OriginalDemandedElts);
+    if (CIdx && CIdx->getAPIntValue().ult(VecVT.getVectorNumElements())) {
+      unsigned Idx = CIdx->getZExtValue();
+      DemandedVecElts.clearBit(Idx);
+
+      // Inserted element is not required.
+      if (!OriginalDemandedElts[Idx])
+        return TLO.CombineTo(Op, Vec);
+    }
+
+    if (!!DemandedVecElts)
+      if (SimplifyDemandedBits(Vec, OriginalDemandedBits, DemandedVecElts,
+                               Known, TLO, Depth + 1))
+        return true;
+
+    KnownBits KnownScl;
+    unsigned NumSclBits = Scl.getScalarValueSizeInBits();
+    APInt DemandedSclBits = OriginalDemandedBits.zextOrTrunc(NumSclBits);
+    if (SimplifyDemandedBits(Scl, DemandedSclBits, KnownScl, TLO, Depth + 1))
+      return true;
+
+    KnownScl = KnownScl.zextOrTrunc(BitWidth, false);
+    Known.One &= KnownScl.One;
+    Known.Zero &= KnownScl.Zero;
+    return false;
+  }
   case ISD::CONCAT_VECTORS: {
     Known.Zero.setAllBits();
     Known.One.setAllBits();
     EVT SubVT = Op.getOperand(0).getValueType();
     unsigned NumSubVecs = Op.getNumOperands();
     unsigned NumSubElts = SubVT.getVectorNumElements();
     for (unsigned i = 0; i != NumSubVecs; ++i) {
       APInt DemandedSubElts =

test/CodeGen/X86/known-signbits-vector.ll

; X64-NEXT:    retq
   ret float %4
 }
 
 define float @signbits_ashr_insert_ashr_extract_sitofp(i64 %a0, i64 %a1) nounwind {
 ; X32-LABEL: signbits_ashr_insert_ashr_extract_sitofp:
 ; X32:       # %bb.0:
 ; X32-NEXT:    pushl %eax
 ; X32-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X32-NEXT:    movl {{[0-9]+}}(%esp), %ecx
-; X32-NEXT:    shrdl $30, %ecx, %eax
+; X32-NEXT:    movl %eax, %ecx
 ; X32-NEXT:    sarl $30, %ecx
+; X32-NEXT:    shll $2, %eax
 ; X32-NEXT:    vmovd %eax, %xmm0
 ; X32-NEXT:    vpinsrd $1, %ecx, %xmm0, %xmm0
 ; X32-NEXT:    vpsrlq $3, %xmm0, %xmm0
 ; X32-NEXT:    vcvtdq2ps %xmm0, %xmm0
 ; X32-NEXT:    vmovss %xmm0, (%esp)
 ; X32-NEXT:    flds (%esp)
 ; X32-NEXT:    popl %eax
 ; X32-NEXT:    retl

test/CodeGen/X86/mulvi32.ll

 ;
 ; the following extractelement's and insertelement's
 ; are just an unrolled 'trunc' plus 'zext' on a vector
 ; %trunc0 = trunc <2 x i64> %0 to <2 x i32>
 ; %trunc1 = trunc <2 x i64> %1 to <2 x i32>
 ; %ext0 = zext <2 x i32> %0 to <2 x i64>
 ; %ext1 = zext <2 x i32> %1 to <2 x i64>
 define <2 x i64> @_mul2xi64toi64a(<2 x i64>, <2 x i64>) {
-; SSE2-LABEL: _mul2xi64toi64a:
-; SSE2:       # %bb.0:
-; SSE2-NEXT:    movdqa {{.*#+}} xmm2 = [4294967295,4294967295]
-; SSE2-NEXT:    pand %xmm2, %xmm0
-; SSE2-NEXT:    pand %xmm2, %xmm1
-; SSE2-NEXT:    pmuludq %xmm1, %xmm0
-; SSE2-NEXT:    retq
-;
-; SSE42-LABEL: _mul2xi64toi64a:
-; SSE42:       # %bb.0:
-; SSE42-NEXT:    pmuludq %xmm1, %xmm0
-; SSE42-NEXT:    retq
+; SSE-LABEL: _mul2xi64toi64a:
+; SSE:       # %bb.0:
+; SSE-NEXT:    pmuludq %xmm1, %xmm0
+; SSE-NEXT:    retq
 ;
 ; AVX-LABEL: _mul2xi64toi64a:
 ; AVX:       # %bb.0:
 ; AVX-NEXT:    vpmuludq %xmm1, %xmm0, %xmm0
 ; AVX-NEXT:    retq
   %f00 = extractelement <2 x i64> %0, i32 0
   %f01 = extractelement <2 x i64> %0, i32 1
   %f10 = extractelement <2 x i64> %1, i32 0

test/CodeGen/X86/vector-shuffle-128-v16.ll

; AVX2OR512VL-NEXT:    retq
   %tmp2 = bitcast <4 x i32> %tmp1 to <16 x i8>
   %tmp3 = shufflevector <16 x i8> %tmp2, <16 x i8> undef, <16 x i32> zeroinitializer
   ret <16 x i8> %tmp3
 }
 
 define <16 x i8> @insert_dup_mem_v16i8_sext_i8(i8* %ptr) {
 ; SSE2-LABEL: insert_dup_mem_v16i8_sext_i8:
 ; SSE2:       # %bb.0:
-; SSE2-NEXT:    movsbl (%rdi), %eax
+; SSE2-NEXT:    movzbl (%rdi), %eax
 ; SSE2-NEXT:    movd %eax, %xmm0
 ; SSE2-NEXT:    punpcklbw {{.*#+}} xmm0 = xmm0[0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7]
 ; SSE2-NEXT:    pshuflw {{.*#+}} xmm0 = xmm0[0,0,2,3,4,5,6,7]
 ; SSE2-NEXT:    pshufd {{.*#+}} xmm0 = xmm0[0,0,0,0]
 ; SSE2-NEXT:    retq
 ;
 ; SSSE3-LABEL: insert_dup_mem_v16i8_sext_i8:
 ; SSSE3:       # %bb.0:
-; SSSE3-NEXT:    movsbl (%rdi), %eax
+; SSSE3-NEXT:    movzbl (%rdi), %eax
 ; SSSE3-NEXT:    movd %eax, %xmm0
 ; SSSE3-NEXT:    pxor %xmm1, %xmm1
 ; SSSE3-NEXT:    pshufb %xmm1, %xmm0
 ; SSSE3-NEXT:    retq
 ;
 ; SSE41-LABEL: insert_dup_mem_v16i8_sext_i8:
 ; SSE41:       # %bb.0:
-; SSE41-NEXT:    movsbl (%rdi), %eax
+; SSE41-NEXT:    movzbl (%rdi), %eax
 ; SSE41-NEXT:    movd %eax, %xmm0
 ; SSE41-NEXT:    pxor %xmm1, %xmm1
 ; SSE41-NEXT:    pshufb %xmm1, %xmm0
 ; SSE41-NEXT:    retq
 ;
 ; AVX1-LABEL: insert_dup_mem_v16i8_sext_i8:
 ; AVX1:       # %bb.0:
-; AVX1-NEXT:    movsbl (%rdi), %eax
+; AVX1-NEXT:    movzbl (%rdi), %eax
 ; AVX1-NEXT:    vmovd %eax, %xmm0
 ; AVX1-NEXT:    vpxor %xmm1, %xmm1, %xmm1
 ; AVX1-NEXT:    vpshufb %xmm1, %xmm0, %xmm0
 ; AVX1-NEXT:    retq
 ;
 ; AVX2OR512VL-LABEL: insert_dup_mem_v16i8_sext_i8:
 ; AVX2OR512VL:       # %bb.0:
 ; AVX2OR512VL-NEXT:    vpbroadcastb (%rdi), %xmm0

test/CodeGen/X86/vector-shuffle-128-v8.ll

; AVX2OR512VL-NEXT:    retq
   %tmp2 = bitcast <4 x i32> %tmp1 to <8 x i16>
   %tmp3 = shufflevector <8 x i16> %tmp2, <8 x i16> undef, <8 x i32> zeroinitializer
   ret <8 x i16> %tmp3
 }
 
 define <8 x i16> @insert_dup_mem_v8i16_sext_i16(i16* %ptr) {
 ; SSE-LABEL: insert_dup_mem_v8i16_sext_i16:
 ; SSE:       # %bb.0:
-; SSE-NEXT:    movswl (%rdi), %eax
+; SSE-NEXT:    movzwl (%rdi), %eax
 ; SSE-NEXT:    movd %eax, %xmm0
 ; SSE-NEXT:    pshuflw {{.*#+}} xmm0 = xmm0[0,0,2,3,4,5,6,7]
 ; SSE-NEXT:    pshufd {{.*#+}} xmm0 = xmm0[0,0,0,0]
 ; SSE-NEXT:    retq
 ;
 ; AVX1-LABEL: insert_dup_mem_v8i16_sext_i16:
 ; AVX1:       # %bb.0:
-; AVX1-NEXT:    movswl (%rdi), %eax
+; AVX1-NEXT:    movzwl (%rdi), %eax
 ; AVX1-NEXT:    vmovd %eax, %xmm0
 ; AVX1-NEXT:    vpshuflw {{.*#+}} xmm0 = xmm0[0,0,2,3,4,5,6,7]
 ; AVX1-NEXT:    vpshufd {{.*#+}} xmm0 = xmm0[0,0,0,0]
 ; AVX1-NEXT:    retq
 ;
 ; AVX2-LABEL: insert_dup_mem_v8i16_sext_i16:
 ; AVX2:       # %bb.0:
-; AVX2-NEXT:    movswl (%rdi), %eax
+; AVX2-NEXT:    movzwl (%rdi), %eax
 ; AVX2-NEXT:    vmovd %eax, %xmm0
 ; AVX2-NEXT:    vpbroadcastw %xmm0, %xmm0
 ; AVX2-NEXT:    retq
 ;
 ; AVX512VL-LABEL: insert_dup_mem_v8i16_sext_i16:
 ; AVX512VL:       # %bb.0:
-; AVX512VL-NEXT:    movswl (%rdi), %eax
+; AVX512VL-NEXT:    movzwl (%rdi), %eax
 ; AVX512VL-NEXT:    vpbroadcastw %eax, %xmm0
 ; AVX512VL-NEXT:    retq
   %tmp = load i16, i16* %ptr, align 2
   %tmp1 = sext i16 %tmp to i32
   %tmp2 = insertelement <4 x i32> zeroinitializer, i32 %tmp1, i32 0
   %tmp3 = bitcast <4 x i32> %tmp2 to <8 x i16>
   %tmp4 = shufflevector <8 x i16> %tmp3, <8 x i16> undef, <8 x i32> zeroinitializer
   ret <8 x i16> %tmp4

test/CodeGen/X86/vector-shuffle-256-v16.ll

; AVX2OR512VL-NEXT:    retq
   %tmp2 = bitcast <4 x i32> %tmp1 to <8 x i16>
   %tmp3 = shufflevector <8 x i16> %tmp2, <8 x i16> undef, <16 x i32> zeroinitializer
   ret <16 x i16> %tmp3
 }
 
 define <16 x i16> @insert_dup_mem_v16i16_sext_i16(i16* %ptr) {
 ; AVX1-LABEL: insert_dup_mem_v16i16_sext_i16:
 ; AVX1:       # %bb.0:
-; AVX1-NEXT:    movswl (%rdi), %eax
+; AVX1-NEXT:    movzwl (%rdi), %eax
 ; AVX1-NEXT:    vmovd %eax, %xmm0
 ; AVX1-NEXT:    vpshuflw {{.*#+}} xmm0 = xmm0[0,0,2,3,4,5,6,7]
 ; AVX1-NEXT:    vpshufd {{.*#+}} xmm0 = xmm0[0,0,0,0]
 ; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
 ; AVX1-NEXT:    retq
 ;
 ; AVX2-LABEL: insert_dup_mem_v16i16_sext_i16:
 ; AVX2:       # %bb.0:
-; AVX2-NEXT:    movswl (%rdi), %eax
+; AVX2-NEXT:    movzwl (%rdi), %eax
 ; AVX2-NEXT:    vmovd %eax, %xmm0
 ; AVX2-NEXT:    vpbroadcastw %xmm0, %ymm0
 ; AVX2-NEXT:    retq
 ;
 ; AVX512VL-LABEL: insert_dup_mem_v16i16_sext_i16:
 ; AVX512VL:       # %bb.0:
-; AVX512VL-NEXT:    movswl (%rdi), %eax
+; AVX512VL-NEXT:    movzwl (%rdi), %eax
 ; AVX512VL-NEXT:    vpbroadcastw %eax, %ymm0
 ; AVX512VL-NEXT:    retq
   %tmp = load i16, i16* %ptr, align 2
   %tmp1 = sext i16 %tmp to i32
   %tmp2 = insertelement <4 x i32> zeroinitializer, i32 %tmp1, i32 0
   %tmp3 = bitcast <4 x i32> %tmp2 to <8 x i16>
   %tmp4 = shufflevector <8 x i16> %tmp3, <8 x i16> undef, <16 x i32> zeroinitializer
   ret <16 x i16> %tmp4

test/CodeGen/X86/vector-shuffle-256-v32.ll

; AVX2OR512VL-NEXT:    retq
   %tmp2 = bitcast <4 x i32> %tmp1 to <16 x i8>
   %tmp3 = shufflevector <16 x i8> %tmp2, <16 x i8> undef, <32 x i32> zeroinitializer
   ret <32 x i8> %tmp3
 }
 
 define <32 x i8> @insert_dup_mem_v32i8_sext_i8(i8* %ptr) {
 ; AVX1-LABEL: insert_dup_mem_v32i8_sext_i8:
 ; AVX1:       # %bb.0:
-; AVX1-NEXT:    movsbl (%rdi), %eax
+; AVX1-NEXT:    movzbl (%rdi), %eax
 ; AVX1-NEXT:    vmovd %eax, %xmm0
 ; AVX1-NEXT:    vpxor %xmm1, %xmm1, %xmm1
 ; AVX1-NEXT:    vpshufb %xmm1, %xmm0, %xmm0
 ; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
 ; AVX1-NEXT:    retq
 ;
 ; AVX2OR512VL-LABEL: insert_dup_mem_v32i8_sext_i8:
 ; AVX2OR512VL:       # %bb.0:

test/CodeGen/X86/vector-shuffle-512-v32.ll

; SKX-NEXT:    retq
   %tmp2 = bitcast <4 x i32> %tmp1 to <8 x i16>
   %tmp3 = shufflevector <8 x i16> %tmp2, <8 x i16> undef, <32 x i32> zeroinitializer
   ret <32 x i16> %tmp3
 }
 
 define <32 x i16> @insert_dup_mem_v32i16_sext_i16(i16* %ptr) {
 ; KNL-LABEL: insert_dup_mem_v32i16_sext_i16:
 ; KNL:       ## %bb.0:
-; KNL-NEXT:    movswl (%rdi), %eax
+; KNL-NEXT:    movzwl (%rdi), %eax
 ; KNL-NEXT:    vmovd %eax, %xmm0
 ; KNL-NEXT:    vpbroadcastw %xmm0, %ymm0
 ; KNL-NEXT:    vmovdqa %ymm0, %ymm1
 ; KNL-NEXT:    retq
 ;
 ; SKX-LABEL: insert_dup_mem_v32i16_sext_i16:
 ; SKX:       ## %bb.0:
-; SKX-NEXT:    movswl (%rdi), %eax
+; SKX-NEXT:    movzwl (%rdi), %eax
 ; SKX-NEXT:    vpbroadcastw %eax, %zmm0
 ; SKX-NEXT:    retq
   %tmp = load i16, i16* %ptr, align 2
   %tmp1 = sext i16 %tmp to i32
   %tmp2 = insertelement <4 x i32> zeroinitializer, i32 %tmp1, i32 0
   %tmp3 = bitcast <4 x i32> %tmp2 to <8 x i16>
   %tmp4 = shufflevector <8 x i16> %tmp3, <8 x i16> undef, <32 x i32> zeroinitializer
   ret <32 x i16> %tmp4