[clang] [clang][CodeGen] `sret` args should always point to the `alloca` AS, so use that (PR #114062)

[Matt Arsenault via cfe-commits]

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@@ -5389,11 +5389,22 @@ RValue CodeGenFunction::EmitCall(const CGFunctionInfo &CallInfo,
             V->getType()->isIntegerTy())
           V = Builder.CreateZExt(V, ArgInfo.getCoerceToType());
 
-        // If the argument doesn't match, perform a bitcast to coerce it.  This
-        // can happen due to trivial type mismatches.
+        // The only plausible mismatch here would be for pointer address spaces,
+        // which can happen e.g. when passing a sret arg that is in the AllocaAS
+        // to a function that takes a pointer to and argument in the DefaultAS.
+        // We assume that the target has a reasonable mapping for the DefaultAS
+        // (it can be casted to from incoming specific ASes), and insert an AS
+        // cast to address the mismatch.
         if (FirstIRArg < IRFuncTy->getNumParams() &&
-            V->getType() != IRFuncTy->getParamType(FirstIRArg))
-          V = Builder.CreateBitCast(V, IRFuncTy->getParamType(FirstIRArg));
+            V->getType() != IRFuncTy->getParamType(FirstIRArg)) {
+          assert(V->getType()->isPointerTy() && "Only pointers can mismatch!");
+          auto FormalAS = CallInfo.arguments()[ArgNo]
+                              .type.getQualifiers()
+                              .getAddressSpace();
+          auto ActualAS = I->Ty.getAddressSpace();
+          V = getTargetHooks().performAddrSpaceCast(
+              *this, V, ActualAS, FormalAS, IRFuncTy->getParamType(FirstIRArg));
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arsenm wrote:

Not sure why a target hook is needed to just insert an addrspacecast, but this seems to be prior art 

https://github.com/llvm/llvm-project/pull/114062