From 83fe1c17821730ac6f0c1c9be7224113b1a1f336 Mon Sep 17 00:00:00 2001
From: Fraser Cormack <fraser@codeplay.com>
Date: Wed, 11 Dec 2024 11:27:36 +0000
Subject: [PATCH] [SYCL][NVPTX] Obey -fcuda-short-ptr when compiling SYCL for
 NVPTX (#15642)

This flag turns pointers to CUDA's `shared`, `const`, and `local`
address spaces into 32-bit pointers. This can potentially save on
registers used for addressing calculations.

This option was being accepted by the frontend when compiling SYCL code,
but was then reporting an error that the backend datalayout doesn't
match the expected target description. This was because the option
wasn't being caught by all parts of the toolchain, leading to
inconsistencies.

This PR allows users to pass the option if they wish. They will see a
warning that the compiler is linking against a libclc/libspirv that
hasn't been compiled with this option, but this is likely harmless since
libspirv doesn't manipulate pointers.
---
 clang/lib/Driver/ToolChains/Clang.cpp      |  3 ++-
 clang/test/CodeGenSYCL/nvptx-short-ptr.cpp | 27 ++++++++++++++++++++++
 clang/test/Driver/sycl-nvptx-short-ptr.cpp | 14 +++++++++++
 3 files changed, 43 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/CodeGenSYCL/nvptx-short-ptr.cpp
 create mode 100644 clang/test/Driver/sycl-nvptx-short-ptr.cpp

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index ad650704a1615..6e08b12196156 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -8593,7 +8593,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     }
   }
 
-  if (IsCuda) {
+  // Propagate -fcuda-short-ptr if compiling CUDA or SYCL for NVPTX
+  if (IsCuda || (IsSYCLDevice && Triple.isNVPTX())) {
     if (Args.hasFlag(options::OPT_fcuda_short_ptr,
                      options::OPT_fno_cuda_short_ptr, false))
       CmdArgs.push_back("-fcuda-short-ptr");
diff --git a/clang/test/CodeGenSYCL/nvptx-short-ptr.cpp b/clang/test/CodeGenSYCL/nvptx-short-ptr.cpp
new file mode 100644
index 0000000000000..90db7373eb967
--- /dev/null
+++ b/clang/test/CodeGenSYCL/nvptx-short-ptr.cpp
@@ -0,0 +1,27 @@
+// Check that when we see the expected data layouts for NVPTX when we pass the
+// -nvptx-short-ptr option.
+
+// RUN: %clang_cc1 -fsycl-is-device -disable-llvm-passes \
+// RUN:  -triple nvptx-nvidia-cuda -emit-llvm %s -o - \
+// RUN:    | FileCheck %s --check-prefix CHECK32
+
+// RUN: %clang_cc1 -fsycl-is-device -disable-llvm-passes \
+// RUN:  -triple nvptx-nvidia-cuda -emit-llvm -fcuda-short-ptr -mllvm -nvptx-short-ptr %s -o - \
+// RUN:    | FileCheck %s --check-prefix CHECK32
+
+// RUN: %clang_cc1 -fsycl-is-device -disable-llvm-passes \
+// RUN:  -triple nvptx64-nvidia-cuda -emit-llvm %s -o - \
+// RUN:    | FileCheck %s --check-prefix CHECK64-DEFAULT
+
+// RUN: %clang_cc1 -fsycl-is-device -disable-llvm-passes \
+// RUN:  -triple nvptx64-nvidia-cuda -emit-llvm -fcuda-short-ptr -mllvm -nvptx-short-ptr %s -o - \
+// RUN:    | FileCheck %s --check-prefix CHECK64-SHORT
+
+// Targeting a 32-bit NVPTX, check that we see universal 32-bit pointers (the
+// option changes nothing)
+// CHECK32: target datalayout = "e-p:32:32-i64:64-i128:128-v16:16-v32:32-n16:32:64"
+
+// Targeting a 64-bit NVPTX target, check that we see 32-bit pointers for
+// shared (3), const (4), and local (5) address spaces only.
+// CHECK64-DEFAULT: target datalayout = "e-i64:64-i128:128-v16:16-v32:32-n16:32:64"
+// CHECK64-SHORT: target datalayout = "e-p3:32:32-p4:32:32-p5:32:32-i64:64-i128:128-v16:16-v32:32-n16:32:64"
diff --git a/clang/test/Driver/sycl-nvptx-short-ptr.cpp b/clang/test/Driver/sycl-nvptx-short-ptr.cpp
new file mode 100644
index 0000000000000..e83ba5954d5cf
--- /dev/null
+++ b/clang/test/Driver/sycl-nvptx-short-ptr.cpp
@@ -0,0 +1,14 @@
+// RUN: %clang -### -nocudalib \
+// RUN:   -fsycl -fsycl-targets=nvptx64-nvidia-cuda %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-DEFAULT %s
+
+// RUN: %clang -### -nocudalib \
+// RUN:   -fsycl -fsycl-targets=nvptx64-nvidia-cuda -fcuda-short-ptr %s 2>&1 \
+// RUN: | FileCheck --check-prefix=CHECK-SHORT %s
+
+
+// CHECK-SHORT: "-mllvm" "--nvptx-short-ptr"
+// CHECK-SHORT: "-fcuda-short-ptr"
+
+// CHECK-DEFAULT-NOT: "--nvptx-short-ptr"
+// CHECK-DEFAULT-NOT: "-fcuda-short-ptr"