[llvm] Enable .ptr .global .align attributes for kernel attributes for CUDA (PR #114874)

[Lewis Crawford via llvm-commits]

================
@@ -1600,29 +1600,37 @@ void NVPTXAsmPrinter::emitFunctionParamList(const Function *F, raw_ostream &O) {
 
       if (isKernelFunc) {
         if (PTy) {
-          // Special handling for pointer arguments to kernel
           O << "\t.param .u" << PTySizeInBits << " ";
 
-          if (static_cast<NVPTXTargetMachine &>(TM).getDrvInterface() !=
-              NVPTX::CUDA) {
-            int addrSpace = PTy->getAddressSpace();
-            switch (addrSpace) {
-            default:
-              O << ".ptr ";
-              break;
-            case ADDRESS_SPACE_CONST:
-              O << ".ptr .const ";
-              break;
-            case ADDRESS_SPACE_SHARED:
-              O << ".ptr .shared ";
-              break;
-            case ADDRESS_SPACE_GLOBAL:
-              O << ".ptr .global ";
-              break;
-            }
-            Align ParamAlign = I->getParamAlign().valueOrOne();
-            O << ".align " << ParamAlign.value() << " ";
+          int addrSpace = PTy->getAddressSpace();
+          const bool IsCUDA =
+              static_cast<NVPTXTargetMachine &>(TM).getDrvInterface() ==
+              NVPTX::CUDA;
+
+          O << ".ptr ";
+          switch (addrSpace) {
+          default:
+            // Special handling for pointer arguments to kernel
+            // CUDA kernels assume that pointers are in global address space
+            // See:
+            // https://docs.nvidia.com/cuda/parallel-thread-execution/index.html#parameter-state-space
+            if (IsCUDA)
+              O << " .global ";
+            break;
+          case ADDRESS_SPACE_CONST:
+            O << " .const ";
+            break;
+          case ADDRESS_SPACE_SHARED:
+            O << " .shared ";
+            break;
+          case ADDRESS_SPACE_GLOBAL:
+            O << " .global ";
+            break;
           }
+
+          Align ParamAlign = I->getParamAlign().valueOrOne();
+          if (ParamAlign != 1 || !IsCUDA)
----------------
LewisCrawford wrote:

Discussion of emitting 1 by default for CL is on the review here: https://reviews.llvm.org/D118894
Clang should emit explicit alignment anyway, so it mostly only impacts other frontends like XLA or Julia (potentially). It maybe makes sense to keep that behaviour for CL there for maximum compatibility, but choose the potentially faster default alignment on CUDA.

https://github.com/llvm/llvm-project/pull/114874