[PATCH] D36938: [X86] When selecting sse_load_f32/f64 pattern, make sure there's only one use of every node all the way back to the root of the match

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.

With masked operations, its possible for the operation node like fadd, fsub, etc. to be used by multiple different vselects. Since the pattern matching will start at the vselect, we need to make sure the operation node itself is only used once before we can fold a load. Otherwise we'll end up folding the same load into multiple instructions.


https://reviews.llvm.org/D36938

Files:
  lib/Target/X86/X86ISelDAGToDAG.cpp
  test/CodeGen/X86/avx512-memfold.ll


Index: test/CodeGen/X86/avx512-memfold.ll
===================================================================
--- test/CodeGen/X86/avx512-memfold.ll
+++ test/CodeGen/X86/avx512-memfold.ll
@@ -72,9 +72,10 @@
 define <4 x float> @test_mask_add_ss_double_use(<4 x float> %a, float* %b, i8 %mask, <4 x float> %c) {
 ; CHECK-LABEL: test_mask_add_ss_double_use:
 ; CHECK:       ## BB#0:
+; CHECK-NEXT:    vmovss {{.*#+}} xmm2 = mem[0],zero,zero,zero
 ; CHECK-NEXT:    kmovw %esi, %k1
-; CHECK-NEXT:    vaddss (%rdi), %xmm0, %xmm1 {%k1}
-; CHECK-NEXT:    vaddss (%rdi), %xmm0, %xmm0 {%k1} {z}
+; CHECK-NEXT:    vaddss %xmm2, %xmm0, %xmm1 {%k1}
+; CHECK-NEXT:    vaddss %xmm2, %xmm0, %xmm0 {%k1} {z}
 ; CHECK-NEXT:    vmulps %xmm0, %xmm1, %xmm0
 ; CHECK-NEXT:    retq
   %b.val = load float, float* %b
Index: lib/Target/X86/X86ISelDAGToDAG.cpp
===================================================================
--- lib/Target/X86/X86ISelDAGToDAG.cpp
+++ lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -1538,6 +1538,19 @@
   return true;
 }
 
+// Make sure this node has one path back to Root. Otherwise its not legal
+// to fold the load.
+static bool hasSingleUsesFromRoot(SDNode *Root, SDNode *N) {
+  SDNode *User = *N->use_begin();
+  while (User != Root) {
+    if (!User->hasOneUse())
+      return false;
+    User = *User->use_begin();
+  }
+
+  return true;
+}
+
 /// Match a scalar SSE load. In particular, we want to match a load whose top
 /// elements are either undef or zeros. The load flavor is derived from the
 /// type of N, which is either v4f32 or v2f64.
@@ -1554,7 +1567,8 @@
   if (ISD::isNON_EXTLoad(N.getNode())) {
     PatternNodeWithChain = N;
     if (IsProfitableToFold(PatternNodeWithChain, N.getNode(), Root) &&
-        IsLegalToFold(PatternNodeWithChain, *N->use_begin(), Root, OptLevel)) {
+        IsLegalToFold(PatternNodeWithChain, *N->use_begin(), Root, OptLevel) &&
+        hasSingleUsesFromRoot(Root, N.getNode())) {
       LoadSDNode *LD = cast<LoadSDNode>(PatternNodeWithChain);
       return selectAddr(LD, LD->getBasePtr(), Base, Scale, Index, Disp,
                         Segment);
@@ -1565,7 +1579,8 @@
   if (N.getOpcode() == X86ISD::VZEXT_LOAD) {
     PatternNodeWithChain = N;
     if (IsProfitableToFold(PatternNodeWithChain, N.getNode(), Root) &&
-        IsLegalToFold(PatternNodeWithChain, *N->use_begin(), Root, OptLevel)) {
+        IsLegalToFold(PatternNodeWithChain, *N->use_begin(), Root, OptLevel) &&
+        hasSingleUsesFromRoot(Root, N.getNode())) {
       auto *MI = cast<MemIntrinsicSDNode>(PatternNodeWithChain);
       return selectAddr(MI, MI->getBasePtr(), Base, Scale, Index, Disp,
                         Segment);
@@ -1579,7 +1594,8 @@
     PatternNodeWithChain = N.getOperand(0);
     if (ISD::isNON_EXTLoad(PatternNodeWithChain.getNode()) &&
         IsProfitableToFold(PatternNodeWithChain, N.getNode(), Root) &&
-        IsLegalToFold(PatternNodeWithChain, N.getNode(), Root, OptLevel)) {
+        IsLegalToFold(PatternNodeWithChain, N.getNode(), Root, OptLevel) &&
+        hasSingleUsesFromRoot(Root, N.getNode())) {
       LoadSDNode *LD = cast<LoadSDNode>(PatternNodeWithChain);
       return selectAddr(LD, LD->getBasePtr(), Base, Scale, Index, Disp,
                         Segment);
@@ -1595,7 +1611,8 @@
     PatternNodeWithChain = N.getOperand(0).getOperand(0);
     if (ISD::isNON_EXTLoad(PatternNodeWithChain.getNode()) &&
         IsProfitableToFold(PatternNodeWithChain, N.getNode(), Root) &&
-        IsLegalToFold(PatternNodeWithChain, N.getNode(), Root, OptLevel)) {
+        IsLegalToFold(PatternNodeWithChain, N.getNode(), Root, OptLevel) &&
+        hasSingleUsesFromRoot(Root, N.getNode())) {
       // Okay, this is a zero extending load.  Fold it.
       LoadSDNode *LD = cast<LoadSDNode>(PatternNodeWithChain);
       return selectAddr(LD, LD->getBasePtr(), Base, Scale, Index, Disp,


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