[llvm] [VectorCombine] Use isSafeToSpeculativelyExecute to guard VP scalarization (PR #69494)

[Luke Lau via llvm-commits]

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@@ -825,23 +825,28 @@ bool VectorCombine::scalarizeVPIntrinsic(Instruction &I) {
   ElementCount EC = cast<VectorType>(Op0->getType())->getElementCount();
   Value *EVL = VPI.getArgOperand(3);
   const DataLayout &DL = VPI.getModule()->getDataLayout();
-  bool MustHaveNonZeroVL =
-      IntrID == Intrinsic::vp_sdiv || IntrID == Intrinsic::vp_udiv ||
-      IntrID == Intrinsic::vp_srem || IntrID == Intrinsic::vp_urem;
-
-  if (!MustHaveNonZeroVL || isKnownNonZero(EVL, DL, 0, &AC, &VPI, &DT)) {
-    Value *ScalarOp0 = getSplatValue(Op0);
-    Value *ScalarOp1 = getSplatValue(Op1);
-    Value *ScalarVal =
-        ScalarIntrID
-            ? Builder.CreateIntrinsic(VecTy->getScalarType(), *ScalarIntrID,
-                                      {ScalarOp0, ScalarOp1})
-            : Builder.CreateBinOp((Instruction::BinaryOps)(*FunctionalOpcode),
-                                  ScalarOp0, ScalarOp1);
-    replaceValue(VPI, *Builder.CreateVectorSplat(EC, ScalarVal));
-    return true;
-  }
-  return false;
+
+  bool SafeToSpeculate;
+  if (ScalarIntrID)
+    SafeToSpeculate = Intrinsic::getAttributes(I.getContext(), *ScalarIntrID)
+                          .hasFnAttr(Attribute::AttrKind::Speculatable);
+  else
+    SafeToSpeculate = isSafeToSpeculativelyExecuteWithOpcode(
+        *FunctionalOpcode, &VPI, nullptr, &AC, &DT);
+  if (!SafeToSpeculate && !isKnownNonZero(EVL, DL, 0, &AC, &VPI, &DT))
----------------
lukel97 wrote:

The idea being that we need to guard against introducing poison/UB that wasn't there before, e.g. if the EVL is zero and the divisor is zero, then there's actually no UB. So we can't scalarize it because then the scalarized version would have UB but the original wouldn't

https://github.com/llvm/llvm-project/pull/69494