[llvm] [X86] Enforce strict pre-legalization to combine in scalarizeExtEltFP (PR #117681)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: None (abhishek-kaushik22)

<details>
<summary>Changes</summary>

Use a `DCI` object to actually check the DAG combine level instead of using the type `i1` because this assumption fails on AVX512 where we have types like `v8i1` after legalization.

---
Full diff: https://github.com/llvm/llvm-project/pull/117681.diff


1 Files Affected:

- (modified) llvm/lib/Target/X86/X86ISelLowering.cpp (+7-6) 


``````````diff
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index e4533570f75086..365ae660ea91e8 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -45842,7 +45842,8 @@ static SDValue combineExtractWithShuffle(SDNode *N, SelectionDAG &DAG,
 /// Extracting a scalar FP value from vector element 0 is free, so extract each
 /// operand first, then perform the math as a scalar op.
 static SDValue scalarizeExtEltFP(SDNode *ExtElt, SelectionDAG &DAG,
-                                 const X86Subtarget &Subtarget) {
+                                 const X86Subtarget &Subtarget,
+                                 TargetLowering::DAGCombinerInfo &DCI) {
   assert(ExtElt->getOpcode() == ISD::EXTRACT_VECTOR_ELT && "Expected extract");
   SDValue Vec = ExtElt->getOperand(0);
   SDValue Index = ExtElt->getOperand(1);
@@ -45877,10 +45878,10 @@ static SDValue scalarizeExtEltFP(SDNode *ExtElt, SelectionDAG &DAG,
   // Vector FP selects don't fit the pattern of FP math ops (because the
   // condition has a different type and we have to change the opcode), so deal
   // with those here.
-  // FIXME: This is restricted to pre type legalization by ensuring the setcc
-  // has i1 elements. If we loosen this we need to convert vector bool to a
-  // scalar bool.
-  if (Vec.getOpcode() == ISD::VSELECT &&
+  // FIXME: This is restricted to pre type legalization. If we loosen this we
+  // need to convert vector bool to a scalar bool.
+  if (DCI.getDAGCombineLevel() < llvm::AfterLegalizeTypes &&
+      Vec.getOpcode() == ISD::VSELECT &&
       Vec.getOperand(0).getOpcode() == ISD::SETCC &&
       Vec.getOperand(0).getValueType().getScalarType() == MVT::i1 &&
       Vec.getOperand(0).getOperand(0).getValueType() == VecVT) {
@@ -46242,7 +46243,7 @@ static SDValue combineExtractVectorElt(SDNode *N, SelectionDAG &DAG,
   if (SDValue V = combineArithReduction(N, DAG, Subtarget))
     return V;
 
-  if (SDValue V = scalarizeExtEltFP(N, DAG, Subtarget))
+  if (SDValue V = scalarizeExtEltFP(N, DAG, Subtarget, DCI))
     return V;
 
   if (CIdx)

``````````

</details>


https://github.com/llvm/llvm-project/pull/117681