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

[Pierre van Houtryve via llvm-commits]

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@@ -676,6 +676,16 @@ multiclass IMAD32_Pats <VOP3_Pseudo inst> {
         (ThreeOpFragSDAG<mul, add> i32:$src0, i32:$src1, (i32 imm:$src2)),
         (EXTRACT_SUBREG (inst $src0, $src1, (i64 (as_i64imm $src2)), 0 /* clamp */), sub0)
         >;
+
+  // Handle cases where amdgpu-codegenprepare-mul24 made a mul24 instead of a normal mul.
+  def : GCNPat <
+      (i64 (add (i64 (AMDGPUmul_u24 i32:$src0, i32:$src1)), i64:$src2)),
+      (inst $src0, $src1, $src2, 0 /* clamp */)
+      >;
+  def : GCNPat <
+      (i64 (add (i64 (zext (i32 (AMDGPUmul_u24 i32:$src0, i32:$src1)))), i64:$src2)),
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Pierre-vh wrote:

Should we do an extract_subreg and fill the upper 32 bits with zero in the result instruction then?

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