[llvm] AMDGPU: Add codegen for atomicrmw operations usub_cond and usub_sat (PR #141068)

[Matt Arsenault via llvm-commits]

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@@ -1089,7 +1089,31 @@ multiclass DSAtomicRetNoRetPat_mc<DS_Pseudo inst, DS_Pseudo noRetInst,
   }
 }
 
+multiclass DSAtomicRetNoRetPatCondSub_mc<DS_Pseudo inst, DS_Pseudo noRetInst,
+                                         ValueType vt, string frag> {
+  let OtherPredicates = [LDSRequiresM0Init] in {
+    def : DSAtomicRetPat<inst, vt,
+                         !cast<PatFrag>(frag#"_local_m0_"#vt)>;
+    def : DSAtomicRetPat<noRetInst, vt,
+                         !cast<PatFrag>(frag#"_local_m0_noret_"#vt), /* complexity */ 1>;
+  }
+
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arsenm wrote:

Is this dead? Weren't these only introduced after gfx9? 

https://github.com/llvm/llvm-project/pull/141068