[llvm-branch-commits] [llvm] [PatternMatch] match splats from an all-zeroes shufflevector (PR #226190)

[Nikita Popov via llvm-branch-commits]

================
@@ -218,14 +218,28 @@ template <typename SubPattern_t> struct Splat_match {
       auto *Splat = C->getSplatValue();
       return Splat ? SubPattern.match(Splat) : false;
     }
-    // TODO: Extend to other cases (e.g. shufflevectors).
-    return false;
+
+    auto *Shuffle = dyn_cast<ShuffleVectorInst>(V);
+    if (!Shuffle || !Shuffle->isZeroEltSplat())
+      return false;
+
+    // Look for an insertelement.
+    auto *Insert = dyn_cast<InsertElementInst>(Shuffle->getOperand(0));
+    if (!Insert)
+      return false;
+
+    Value *SplatElt = Insert->getOperand(1);
+    ConstantInt *Idx = dyn_cast<ConstantInt>(Insert->getOperand(2));
+    if (!Idx || Idx->getZExtValue() != 0)
----------------
nikic wrote:

```suggestion
    if (!Idx || !Idx->isZero())
```
To not risk an assertion failure for overly large indices.

https://github.com/llvm/llvm-project/pull/226190