[x86, dag] Teach the DAG combiner to prune inputs toa vector_shuffle

that are unused.

This allows the combiner to delete math feeding shuffles where the math
isn't actually necessary. This improves some of the vperm2x128 tests
that regressed when the vector shuffle lowering started actually
generating vperm instructions rather than forcibly decomposing them.

Sadly, this isn't enough to get this *really* right because we still
form a completely unnecessary permutation. To fix that, we also need to
fold shuffles which just rearrange concatenated or inserted subvectors.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219086 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 03a1b71407ee160b672f2b6c26258aab82b14b62..d8d3380e92834a528fb34c525292677f7d36c49e 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -17,6 +17,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/SelectionDAG.h"
+#include "llvm/ADT/SmallBitVector.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/Statistic.h"
@@ -10708,6 +10709,92 @@ SDValue DAGCombiner::visitEXTRACT_SUBVECTOR(SDNode* N) {
   return SDValue();
 }
 
+static SDValue simplifyShuffleOperandRecursively(SmallBitVector &UsedElements,
+                                                 SDValue V, SelectionDAG &DAG) {
+  SDLoc DL(V);
+  EVT VT = V.getValueType();
+
+  switch (V.getOpcode()) {
+  default:
+    return V;
+
+  case ISD::CONCAT_VECTORS: {
+    EVT OpVT = V->getOperand(0).getValueType();
+    int OpSize = OpVT.getVectorNumElements();
+    SmallBitVector OpUsedElements(OpSize, false);
+    bool FoundSimplification = false;
+    SmallVector<SDValue, 4> NewOps;
+    NewOps.reserve(V->getNumOperands());
+    for (int i = 0, NumOps = V->getNumOperands(); i < NumOps; ++i) {
+      SDValue Op = V->getOperand(i);
+      bool OpUsed = false;
+      for (int j = 0; j < OpSize; ++j)
+        if (UsedElements[i * OpSize + j]) {
+          OpUsedElements[j] = true;
+          OpUsed = true;
+        }
+      NewOps.push_back(
+          OpUsed ? simplifyShuffleOperandRecursively(OpUsedElements, Op, DAG)
+                 : DAG.getUNDEF(OpVT));
+      FoundSimplification |= Op == NewOps.back();
+      OpUsedElements.reset();
+    }
+    if (FoundSimplification)
+      V = DAG.getNode(ISD::CONCAT_VECTORS, DL, VT, NewOps);
+    return V;
+  }
+
+  case ISD::INSERT_SUBVECTOR: {
+    SDValue BaseV = V->getOperand(0);
+    SDValue SubV = V->getOperand(1);
+    auto *IdxN = dyn_cast<ConstantSDNode>(V->getOperand(2));
+    if (!IdxN)
+      return V;
+
+    int SubSize = SubV.getValueType().getVectorNumElements();
+    int Idx = IdxN->getZExtValue();
+    bool SubVectorUsed = false;
+    SmallBitVector SubUsedElements(SubSize, false);
+    for (int i = 0; i < SubSize; ++i)
+      if (UsedElements[i + Idx]) {
+        SubVectorUsed = true;
+        SubUsedElements[i] = true;
+        UsedElements[i + Idx] = false;
+      }
+
+    // Now recurse on both the base and sub vectors.
+    SDValue SimplifiedSubV =
+        SubVectorUsed
+            ? simplifyShuffleOperandRecursively(SubUsedElements, SubV, DAG)
+            : DAG.getUNDEF(SubV.getValueType());
+    SDValue SimplifiedBaseV = simplifyShuffleOperandRecursively(UsedElements, BaseV, DAG);
+    if (SimplifiedSubV != SubV || SimplifiedBaseV != BaseV)
+      V = DAG.getNode(ISD::INSERT_SUBVECTOR, DL, VT,
+                      SimplifiedBaseV, SimplifiedSubV, V->getOperand(2));
+    return V;
+  }
+  }
+}
+
+static SDValue simplifyShuffleOperands(ShuffleVectorSDNode *SVN, SDValue N0,
+                                       SDValue N1, SelectionDAG &DAG) {
+  EVT VT = SVN->getValueType(0);
+  int NumElts = VT.getVectorNumElements();
+  SmallBitVector N0UsedElements(NumElts, false), N1UsedElements(NumElts, false);
+  for (int M : SVN->getMask())
+    if (M >= 0 && M < NumElts)
+      N0UsedElements[M] = true;
+    else if (M >= NumElts)
+      N1UsedElements[M - NumElts] = true;
+
+  SDValue S0 = simplifyShuffleOperandRecursively(N0UsedElements, N0, DAG);
+  SDValue S1 = simplifyShuffleOperandRecursively(N1UsedElements, N1, DAG);
+  if (S0 == N0 && S1 == N1)
+    return SDValue();
+
+  return DAG.getVectorShuffle(VT, SDLoc(SVN), S0, S1, SVN->getMask());
+}
+
 // Tries to turn a shuffle of two CONCAT_VECTORS into a single concat.
 static SDValue partitionShuffleOfConcats(SDNode *N, SelectionDAG &DAG) {
   EVT VT = N->getValueType(0);
@@ -10860,6 +10947,12 @@ SDValue DAGCombiner::visitVECTOR_SHUFFLE(SDNode *N) {
     }
   }
 
+  // There are various patterns used to build up a vector from smaller vectors,
+  // subvectors, or elements. Scan chains of these and replace unused insertions
+  // or components with undef.
+  if (SDValue S = simplifyShuffleOperands(SVN, N0, N1, DAG))
+    return S;
+
   if (N0.getOpcode() == ISD::CONCAT_VECTORS &&
       Level < AfterLegalizeVectorOps &&
       (N1.getOpcode() == ISD::UNDEF ||

diff --git a/test/CodeGen/X86/avx-vperm2x128.ll b/test/CodeGen/X86/avx-vperm2x128.ll
index fa554e9785658ef345a55bc8e2fc93be74349f62..5afdcabe7f6ec59aac6286a537b17b234a2a0ba5 100644 (file)
--- a/test/CodeGen/X86/avx-vperm2x128.ll
+++ b/test/CodeGen/X86/avx-vperm2x128.ll
@@ -64,11 +64,9 @@ entry:
 define <32 x i8> @Ei(<32 x i8> %a, <32 x i8> %b) nounwind uwtable readnone ssp {
 ; AVX1-LABEL: Ei:
 ; AVX1:       ## BB#0: ## %entry
-; AVX1-NEXT:    vextractf128 $1, %ymm0, %xmm1
-; AVX1-NEXT:    vmovdqa {{.*#+}} xmm2 = [1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1]
-; AVX1-NEXT:    vpaddb %xmm2, %xmm1, %xmm1
-; AVX1-NEXT:    vpaddb %xmm2, %xmm0, %xmm0
-; AVX1-NEXT:    vinsertf128 $1, %xmm1, %ymm0, %ymm0
+; AVX1-NEXT:    vextractf128 $1, %ymm0, %xmm0
+; AVX1-NEXT:    vpaddb {{.*}}(%rip), %xmm0, %xmm0
+; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
 ; AVX1-NEXT:    vperm2f128 {{.*#+}} ymm0 = ymm0[2,3,2,3]
 ; AVX1-NEXT:    retq
 ;
@@ -87,11 +85,7 @@ entry:
 define <4 x i64> @E2i(<4 x i64> %a, <4 x i64> %b) nounwind uwtable readnone ssp {
 ; AVX1-LABEL: E2i:
 ; AVX1:       ## BB#0: ## %entry
-; AVX1-NEXT:    vextractf128 $1, %ymm0, %xmm2
-; AVX1-NEXT:    vmovdqa {{.*#+}} xmm3 = [1,1]
-; AVX1-NEXT:    vpaddq %xmm3, %xmm2, %xmm2
-; AVX1-NEXT:    vpaddq %xmm3, %xmm0, %xmm0
-; AVX1-NEXT:    vinsertf128 $1, %xmm2, %ymm0, %ymm0
+; AVX1-NEXT:    vpaddq {{.*}}(%rip), %xmm0, %xmm0
 ; AVX1-NEXT:    vperm2f128 {{.*#+}} ymm0 = ymm1[2,3],ymm0[0,1]
 ; AVX1-NEXT:    retq
 ;
@@ -111,11 +105,9 @@ entry:
 define <8 x i32> @E3i(<8 x i32> %a, <8 x i32> %b) nounwind uwtable readnone ssp {
 ; AVX1-LABEL: E3i:
 ; AVX1:       ## BB#0: ## %entry
-; AVX1-NEXT:    vextractf128 $1, %ymm0, %xmm2
-; AVX1-NEXT:    vmovdqa {{.*#+}} xmm3 = [1,1,1,1]
-; AVX1-NEXT:    vpaddd %xmm3, %xmm2, %xmm2
-; AVX1-NEXT:    vpaddd %xmm3, %xmm0, %xmm0
-; AVX1-NEXT:    vinsertf128 $1, %xmm2, %ymm0, %ymm0
+; AVX1-NEXT:    vextractf128 $1, %ymm0, %xmm0
+; AVX1-NEXT:    vpaddd {{.*}}(%rip), %xmm0, %xmm0
+; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
 ; AVX1-NEXT:    vperm2f128 {{.*#+}} ymm0 = ymm0[2,3],ymm1[2,3]
 ; AVX1-NEXT:    retq
 ;

diff --git a/test/CodeGen/X86/vector-shuffle-combining.ll b/test/CodeGen/X86/vector-shuffle-combining.ll
index 5822fc915357d31e682fc87b5dcba2fb449bb768..87b05202d9af7cee00eec4db388e1f4bec623bc8 100644 (file)
--- a/test/CodeGen/X86/vector-shuffle-combining.ll
+++ b/test/CodeGen/X86/vector-shuffle-combining.ll
@@ -2512,3 +2512,67 @@ define <4 x float> @combine_undef_input_test20(<4 x float> %a) {
   %2 = shufflevector <4 x float> %a, <4 x float> %1, <4 x i32> <i32 4, i32 6, i32 2, i32 3>
   ret <4 x float> %2
 }
+
+; These tests are designed to test the ability to combine away unnecessary
+; operations feeding into a shuffle. The AVX cases are the important ones as
+; they leverage operations which cannot be done naturally on the entire vector
+; and thus are decomposed into multiple smaller operations.
+
+define <8 x i32> @combine_unneeded_subvector1(<8 x i32> %a) {
+; SSE-LABEL: combine_unneeded_subvector1:
+; SSE:       # BB#0:
+; SSE-NEXT:    paddd {{.*}}(%rip), %xmm1
+; SSE-NEXT:    pshufd {{.*#+}} xmm0 = xmm1[3,2,1,0]
+; SSE-NEXT:    movdqa %xmm0, %xmm1
+; SSE-NEXT:    retq
+;
+; AVX1-LABEL: combine_unneeded_subvector1:
+; AVX1:       # BB#0:
+; AVX1-NEXT:    vextractf128 $1, %ymm0, %xmm0
+; AVX1-NEXT:    vpaddd {{.*}}(%rip), %xmm0, %xmm0
+; AVX1-NEXT:    vpermilps {{.*#+}} xmm0 = xmm0[3,2,1,0]
+; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
+; AVX1-NEXT:    retq
+;
+; AVX2-LABEL: combine_unneeded_subvector1:
+; AVX2:       # BB#0:
+; AVX2-NEXT:    vpaddd {{.*}}(%rip), %ymm0, %ymm0
+; AVX2-NEXT:    vmovdqa {{.*#+}} ymm1 = [7,6,5,4,7,6,5,4]
+; AVX2-NEXT:    vpermd %ymm0, %ymm1, %ymm0
+; AVX2-NEXT:    retq
+  %b = add <8 x i32> %a, <i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8>
+  %c = shufflevector <8 x i32> %b, <8 x i32> undef, <8 x i32> <i32 7, i32 6, i32 5, i32 4, i32 7, i32 6, i32 5, i32 4>
+  ret <8 x i32> %c
+}
+
+define <8 x i32> @combine_unneeded_subvector2(<8 x i32> %a, <8 x i32> %b) {
+; SSE-LABEL: combine_unneeded_subvector2:
+; SSE:       # BB#0:
+; SSE-NEXT:    paddd {{.*}}(%rip), %xmm1
+; SSE-NEXT:    pshufd {{.*#+}} xmm0 = xmm3[3,2,1,0]
+; SSE-NEXT:    pshufd {{.*#+}} xmm1 = xmm1[3,2,1,0]
+; SSE-NEXT:    retq
+;
+; AVX1-LABEL: combine_unneeded_subvector2:
+; AVX1:       # BB#0:
+; AVX1-NEXT:    vextractf128 $1, %ymm0, %xmm0
+; AVX1-NEXT:    vpaddd {{.*}}(%rip), %xmm0, %xmm0
+; AVX1-NEXT:    vinsertf128 $1, %xmm0, %ymm0, %ymm0
+; AVX1-NEXT:    vextractf128 $1, %ymm1, %xmm1
+; AVX1-NEXT:    vpermilps {{.*#+}} xmm1 = xmm1[3,2,1,0]
+; AVX1-NEXT:    vpermilps {{.*#+}} ymm0 = ymm0[3,2,1,0,7,6,5,4]
+; AVX1-NEXT:    vblendpd {{.*#+}} ymm0 = ymm1[0,1],ymm0[2,3]
+; AVX1-NEXT:    retq
+;
+; AVX2-LABEL: combine_unneeded_subvector2:
+; AVX2:       # BB#0:
+; AVX2-NEXT:    vpaddd {{.*}}(%rip), %ymm0, %ymm0
+; AVX2-NEXT:    vmovdqa {{.*#+}} ymm2 = <7,6,5,4,u,u,u,u>
+; AVX2-NEXT:    vpermd %ymm1, %ymm2, %ymm1
+; AVX2-NEXT:    vpshufd {{.*#+}} ymm0 = ymm0[3,2,1,0,7,6,5,4]
+; AVX2-NEXT:    vpblendd {{.*#+}} ymm0 = ymm1[0,1,2,3],ymm0[4,5,6,7]
+; AVX2-NEXT:    retq
+  %c = add <8 x i32> %a, <i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8>
+  %d = shufflevector <8 x i32> %b, <8 x i32> %c, <8 x i32> <i32 7, i32 6, i32 5, i32 4, i32 15, i32 14, i32 13, i32 12>
+  ret <8 x i32> %d
+}