[llvm] [VectorUtils] Allow trivially vectorising llvm.[su]mulh. (PR #223998)

[Ricardo Jesus via llvm-commits]

https://github.com/rj-jesus created https://github.com/llvm/llvm-project/pull/223998

None

>From b2a6f4531c6c04051fa08436c8933ef92843d344 Mon Sep 17 00:00:00 2001
From: Ricardo Jesus <rjj at nvidia.com>
Date: Wed, 16 Sep 2026 03:44:16 -0700
Subject: [PATCH] [VectorUtils] Allow trivially vectorising llvm.[su]mulh.

---
 llvm/lib/Analysis/VectorUtils.cpp             |  2 +
 .../Transforms/LoopVectorize/intrinsic.ll     | 60 +++++++++++++++++++
 2 files changed, 62 insertions(+)

diff --git a/llvm/lib/Analysis/VectorUtils.cpp b/llvm/lib/Analysis/VectorUtils.cpp
index f28fc4afc70ef..1c105ebb772b3 100644
--- a/llvm/lib/Analysis/VectorUtils.cpp
+++ b/llvm/lib/Analysis/VectorUtils.cpp
@@ -123,6 +123,8 @@ bool llvm::isTriviallyVectorizable(Intrinsic::ID ID) {
   case Intrinsic::ucmp:
   case Intrinsic::scmp:
   case Intrinsic::clmul:
+  case Intrinsic::smulh:
+  case Intrinsic::umulh:
     return true;
   default:
     return false;
diff --git a/llvm/test/Transforms/LoopVectorize/intrinsic.ll b/llvm/test/Transforms/LoopVectorize/intrinsic.ll
index 521f7589838b7..3ea8ec4e9e1c7 100644
--- a/llvm/test/Transforms/LoopVectorize/intrinsic.ll
+++ b/llvm/test/Transforms/LoopVectorize/intrinsic.ll
@@ -1870,3 +1870,63 @@ exit:
   ret void
 
 }
+
+define void @smulh_i64(ptr %a, ptr %b, ptr %c, i64 %n) {
+; CHECK-LABEL: @smulh_i64(
+; CHECK: llvm.smulh.v4i64
+; CHECK: ret void
+;
+entry:
+  br label %for.body
+
+for.body:
+  %i = phi i64 [0, %entry], [%i.next, %for.body]
+
+  %pa = getelementptr i64, ptr %a, i64 %i
+  %pb = getelementptr i64, ptr %b, i64 %i
+  %pc = getelementptr i64, ptr %c, i64 %i
+
+  %va = load i64, ptr %pa
+  %vb = load i64, ptr %pb
+
+  %r = call i64 @llvm.smulh.i64(i64 %va, i64 %vb)
+
+  store i64 %r, ptr %pc
+
+  %i.next = add i64 %i, 1
+  %cmp = icmp eq i64 %i.next, %n
+  br i1 %cmp, label %exit, label %for.body
+
+exit:
+  ret void
+}
+
+define void @umulh_i64(ptr %a, ptr %b, ptr %c, i64 %n) {
+; CHECK-LABEL: @umulh_i64(
+; CHECK: llvm.umulh.v4i64
+; CHECK: ret void
+;
+entry:
+  br label %for.body
+
+for.body:
+  %i = phi i64 [0, %entry], [%i.next, %for.body]
+
+  %pa = getelementptr i64, ptr %a, i64 %i
+  %pb = getelementptr i64, ptr %b, i64 %i
+  %pc = getelementptr i64, ptr %c, i64 %i
+
+  %va = load i64, ptr %pa
+  %vb = load i64, ptr %pb
+
+  %r = call i64 @llvm.umulh.i64(i64 %va, i64 %vb)
+
+  store i64 %r, ptr %pc
+
+  %i.next = add i64 %i, 1
+  %cmp = icmp eq i64 %i.next, %n
+  br i1 %cmp, label %exit, label %for.body
+
+exit:
+  ret void
+}