[llvm] [LLVM][ConstantFolding] Extend constantFoldVectorReduce to include scalable vectors. (PR #165437)

[David Sherwood via llvm-commits]

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@@ -2163,18 +2163,39 @@ Constant *ConstantFoldBinaryFP(double (*NativeFP)(double, double),
 }
 
 Constant *constantFoldVectorReduce(Intrinsic::ID IID, Constant *Op) {
-  FixedVectorType *VT = dyn_cast<FixedVectorType>(Op->getType());
-  if (!VT)
-    return nullptr;
-
-  // This isn't strictly necessary, but handle the special/common case of zero:
-  // all integer reductions of a zero input produce zero.
-  if (isa<ConstantAggregateZero>(Op))
-    return ConstantInt::get(VT->getElementType(), 0);
+  auto *OpVT = cast<VectorType>(Op->getType());
 
   // This is the same as the underlying binops - poison propagates.
   if (isa<PoisonValue>(Op) || Op->containsPoisonElement())
-    return PoisonValue::get(VT->getElementType());
+    return PoisonValue::get(OpVT->getElementType());
+
+  // Shortcut non-accumulating reductions.
+  if (Constant *SplatVal = Op->getSplatValue()) {
+    switch (IID) {
+    case Intrinsic::vector_reduce_and:
+    case Intrinsic::vector_reduce_or:
+    case Intrinsic::vector_reduce_smin:
+    case Intrinsic::vector_reduce_smax:
+    case Intrinsic::vector_reduce_umin:
+    case Intrinsic::vector_reduce_umax:
+      return SplatVal;
+    case Intrinsic::vector_reduce_add:
+    case Intrinsic::vector_reduce_mul:
+      if (SplatVal->isZeroValue())
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david-arm wrote:

In theory you can also do a short cut for a mul reduce with a splat value of 1, if you think it's worth adding?

https://github.com/llvm/llvm-project/pull/165437