[llvm] [X86] Generate `vpmuludq` instead of `vpmullq` (PR #121456)

[Simon Pilgrim via llvm-commits]

================
@@ -0,0 +1,18 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc < %s -mtriple=x86_64-- -mattr=+avx512dq | FileCheck %s
+
+define <8 x i64> @pr121456(<8 x i64> %a, <8 x i64> %b) {
----------------
RKSimon wrote:

Don't call the test file after a pull request - "pr" is the old llvm term for problem report - the number should be based off a reported issue number (is there one?) - otherwise I'd probably suggest adding these tests to combine-pmuldq.ll instead

https://github.com/llvm/llvm-project/pull/121456