[llvm] [AMDGPU] Pass sret pointers in SGPRs (PR #203486)

[Matt Arsenault via llvm-commits]

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@@ -3407,7 +3374,11 @@ bool isArgPassedInSGPR(const Argument *A) {
            A->hasAttribute(Attribute::ByVal);
   default:
     // TODO: treat i1 as divergent?
-    return A->hasAttribute(Attribute::InReg);
+    // sret/byval pointers are a constant offset from the wave-uniform stack
+    // pointer, so they are uniform and passed in SGPRs (see CC_AMDGPU_Func).
+    return A->hasAttribute(Attribute::InReg) ||
+           A->hasAttribute(Attribute::StructRet) ||
+           A->hasAttribute(Attribute::ByVal);
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arsenm wrote:

Title only mentions sret, and the Callingconv patch doesn't cover byval

https://github.com/llvm/llvm-project/pull/203486