[llvm] [InstCombine] Match intrinsic recurrences when known to be hoisted (PR #149858)

[Nikita Popov via llvm-commits]

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@@ -1532,6 +1532,46 @@ static Instruction *foldBitOrderCrossLogicOp(Value *V,
   return nullptr;
 }
 
+static bool foldBinaryIntrinsicRecurrence(InstCombinerImpl &IC,
+                                          IntrinsicInst *II) {
+  PHINode *PN;
+  Value *Init, *OtherOp;
+
+  // A binary intrinsic recurrence with loop-invariant operands is equivalent to
+  // `call @llvm.binary.intrinsic(Init, OtherOp)`.
+  if (!matchSimpleBinaryIntrinsicRecurrence(II, PN, Init, OtherOp) ||
+      isa<Constant>(OtherOp) || !PN->hasOneUse() ||
+      !IC.getDominatorTree().dominates(OtherOp, PN))
+    return false;
+
+  auto IID = II->getIntrinsicID();
+  switch (IID) {
+  case Intrinsic::maxnum:
+  case Intrinsic::minnum:
+  case Intrinsic::maximum:
+  case Intrinsic::minimum:
+  case Intrinsic::maximumnum:
+  case Intrinsic::minimumnum:
+  case Intrinsic::smax:
+  case Intrinsic::smin:
+  case Intrinsic::umax:
+  case Intrinsic::umin:
+    break;
+  default:
+    return false;
+  }
+
+  IC.Builder.SetInsertPoint(&*PN->getParent()->getFirstInsertionPt());
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nikic wrote:

Why insert at the point of the phi node instead of the point of the intrinsic (the default)? That would be safer (no need to worry about edge cases without insertion point).

https://github.com/llvm/llvm-project/pull/149858