[clang] [clang][CodeGen][OpenCL] Fix `alloca` handling & `sret`when compiling for (PR #113930)

[Matt Arsenault via cfe-commits]

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@@ -108,11 +108,15 @@ RawAddress CodeGenFunction::CreateTempAlloca(llvm::Type *Ty, CharUnits Align,
   if (AllocaAddr)
     *AllocaAddr = Alloca;
   llvm::Value *V = Alloca.getPointer();
+  assert((!getLangOpts().OpenCL ||
+          CGM.getTarget().getTargetAddressSpace(getASTAllocaAddressSpace()) ==
+              CGM.getTarget().getTargetAddressSpace(LangAS::opencl_private)) &&
+         "For OpenCL allocas must allocate in the private address space!");
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arsenm wrote:

That is the nature of the PTX hack. They pretend everything is 0, and then fix up stack later. The backend then runs NVPTXLowerAlloca to introduce a bunch of casts to show that it really was an addrspace(5) pointer to begin with around most use contexts 

https://github.com/llvm/llvm-project/pull/113930