[x86][aarch64] ask the backend whether it has a vector blend instruction

The code to match and produce more x86 vector blends was enabled for all
architectures even though the transform may pessimize the code for other
architectures that do not provide a vector blend instruction.

Added an aarch64 testcase to check that a VZIP instruction is generated instead
of byte movs.

Differential Revision: https://reviews.llvm.org/D44118

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327132 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Sebastian Pop

include/llvm/CodeGen/TargetLowering.h

@@ -2117,6 +2117,9 @@ class TargetLoweringBase {
     return false;
   }
 
+  /// Return true if the target has a vector blend instruction.
+  virtual bool hasVectorBlend() const { return false; }
+
   /// \brief Get the maximum supported factor for interleaved memory accesses.
   /// Default to be the minimum interleave factor: 2.
   virtual unsigned getMaxSupportedInterleaveFactor() const { return 2; }

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -1557,33 +1557,35 @@ SDValue SelectionDAG::getVectorShuffle(EVT VT, const SDLoc &dl, SDValue N1,
   if (N1.isUndef())
     commuteShuffle(N1, N2, MaskVec);
 
-  // If shuffling a splat, try to blend the splat instead. We do this here so
-  // that even when this arises during lowering we don't have to re-handle it.
-  auto BlendSplat = [&](BuildVectorSDNode *BV, int Offset) {
-    BitVector UndefElements;
-    SDValue Splat = BV->getSplatValue(&UndefElements);
-    if (!Splat)
-      return;
+  if (TLI->hasVectorBlend()) {
+    // If shuffling a splat, try to blend the splat instead. We do this here so
+    // that even when this arises during lowering we don't have to re-handle it.
+    auto BlendSplat = [&](BuildVectorSDNode *BV, int Offset) {
+      BitVector UndefElements;
+      SDValue Splat = BV->getSplatValue(&UndefElements);
+      if (!Splat)
+        return;
 
-    for (int i = 0; i < NElts; ++i) {
-      if (MaskVec[i] < Offset || MaskVec[i] >= (Offset + NElts))
-        continue;
+      for (int i = 0; i < NElts; ++i) {
+        if (MaskVec[i] < Offset || MaskVec[i] >= (Offset + NElts))
+          continue;
 
-      // If this input comes from undef, mark it as such.
-      if (UndefElements[MaskVec[i] - Offset]) {
-        MaskVec[i] = -1;
-        continue;
-      }
+        // If this input comes from undef, mark it as such.
+        if (UndefElements[MaskVec[i] - Offset]) {
+          MaskVec[i] = -1;
+          continue;
+        }
 
-      // If we can blend a non-undef lane, use that instead.
-      if (!UndefElements[i])
-        MaskVec[i] = i + Offset;
-    }
-  };
-  if (auto *N1BV = dyn_cast<BuildVectorSDNode>(N1))
-    BlendSplat(N1BV, 0);
-  if (auto *N2BV = dyn_cast<BuildVectorSDNode>(N2))
-    BlendSplat(N2BV, NElts);
+        // If we can blend a non-undef lane, use that instead.
+        if (!UndefElements[i])
+          MaskVec[i] = i + Offset;
+      }
+    };
+    if (auto *N1BV = dyn_cast<BuildVectorSDNode>(N1))
+      BlendSplat(N1BV, 0);
+    if (auto *N2BV = dyn_cast<BuildVectorSDNode>(N2))
+      BlendSplat(N2BV, NElts);
+  }
 
   // Canonicalize all index into lhs, -> shuffle lhs, undef
   // Canonicalize all index into rhs, -> shuffle rhs, undef

lib/Target/X86/X86ISelLowering.h

@@ -1098,6 +1098,8 @@ namespace llvm {
 
     StringRef getStackProbeSymbolName(MachineFunction &MF) const override;
 
+    bool hasVectorBlend() const override { return true; }
+
     unsigned getMaxSupportedInterleaveFactor() const override { return 4; }
 
     /// \brief Lower interleaved load(s) into target specific

test/CodeGen/AArch64/aarch64-vuzp.ll

@@ -58,3 +58,13 @@ entry:
   store <4 x i32> %y, <4 x i32>* %z, align 4
   ret void
 }
+
+; Check that this pattern is recognized as a VZIP and
+; that the vector blend transform does not scramble the pattern.
+; CHECK-LABEL: vzipNoBlend:
+; CHECK: zip1
+define <8 x i8> @vzipNoBlend(<8 x i8>* %A, <8 x i16>* %B) nounwind {
+  %t = load <8 x i8>, <8 x i8>* %A
+  %vzip = shufflevector <8 x i8> %t, <8 x i8> <i8 0, i8 0, i8 0, i8 0, i8 undef, i8 undef, i8 undef, i8 undef>, <8 x i32> <i32 0, i32 8, i32 1, i32 9, i32 2, i32 10, i32 3, i32 11>
+  ret <8 x i8> %vzip
+}

test/CodeGen/AArch64/arm64-collect-loh.ll

@@ -638,13 +638,13 @@ define void @setL(<1 x i8> %t) {
 ; CHECK: [[LOH_LABEL1:Lloh[0-9]+]]:
 ; CHECK: ldr q[[IDX:[0-9]+]], {{\[}}[[ADRP_REG]], [[CONSTPOOL]]@PAGEOFF]
 ; The tuple comes from the next instruction.
-; CHECK-NEXT: tbl.16b v{{[0-9]+}}, { v{{[0-9]+}}, v{{[0-9]+}} }, v[[IDX]]
+; CHECK: ext.16b v{{[0-9]+}}, v{{[0-9]+}}, v{{[0-9]+}}, #1
 ; CHECK: ret
 ; CHECK: .loh AdrpLdr [[LOH_LABEL0]], [[LOH_LABEL1]]
 define void @uninterestingSub(i8* nocapture %row) #0 {
   %tmp = bitcast i8* %row to <16 x i8>*
   %tmp1 = load <16 x i8>, <16 x i8>* %tmp, align 16
-  %vext43 = shufflevector <16 x i8> <i8 undef, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0, i8 0>, <16 x i8> %tmp1, <16 x i32> <i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15, i32 16>
+  %vext43 = shufflevector <16 x i8> <i8 undef, i8 16, i8 15, i8 14, i8 13, i8 12, i8 11, i8 10, i8 9, i8 8, i8 7, i8 6, i8 5, i8 4, i8 3, i8 2>, <16 x i8> %tmp1, <16 x i32> <i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9, i32 10, i32 11, i32 12, i32 13, i32 14, i32 15, i32 16>
   %add.i.414 = add <16 x i8> zeroinitializer, %vext43
   store <16 x i8> %add.i.414, <16 x i8>* %tmp, align 16
   %add.ptr51 = getelementptr inbounds i8, i8* %row, i64 16