[llvm] [AMDGPU] Form V_MAD_U64_U32 from mul24 (PR #72393)

[Matt Arsenault via llvm-commits]

================
@@ -678,9 +678,26 @@ multiclass IMAD32_Pats <VOP3_Pseudo inst> {
         >;
 }
 
+// Handle cases where amdgpu-codegenprepare-mul24 made a mul24 instead of a normal mul.
+// We need to separate this because otherwise OtherPredicates would be overriden.
+multiclass IMAD32_Mul24_Pats <VOP3_Pseudo inst> {
+  def : GCNPat <
+      (i64 (add (i64 (AMDGPUmul_u24 i32:$src0, i32:$src1)), i64:$src2)),
+      (inst $src0, $src1, $src2, 0 /* clamp */)
+      >;
----------------
arsenm wrote:

Don't see how the speed model matters here 

https://github.com/llvm/llvm-project/pull/72393