[PATCH] D106401: [CUDA, MemCpyOpt] Add a flag to force-enable memcpyopt and use it for CUDA.

[Artem Belevich via Phabricator via llvm-commits]

tra created this revision.
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Attempt to enable MemCpyOpt unconditionally in D104801 <https://reviews.llvm.org/D104801> uncovered the fact that
there are users that do not expect LLVM to materialize `memset` intrinsic.

While other passes can do that, too, MemCpyOpt triggers it more frequently and breaks sanitizers and
some downstream users.

For now introduce a flag to force-enable the flag and opt-in only CUDA
compilation with NVPTX back-end.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D106401

Files:
  clang/lib/Driver/ToolChains/Cuda.cpp
  llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp


Index: llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -67,6 +67,10 @@
 
 #define DEBUG_TYPE "memcpyopt"
 
+static cl::opt<bool> EnableMemCpyOptWithoutLibcalls(
+    "-enable-memcpyopt-without-libcalls", cl::init(false), cl::Hidden,
+    cl::desc("Enable memcpyopt even when libcalls are disabled"));
+
 static cl::opt<bool>
     EnableMemorySSA("enable-memcpyopt-memoryssa", cl::init(true), cl::Hidden,
                     cl::desc("Use MemorySSA-backed MemCpyOpt."));
@@ -1757,7 +1761,16 @@
   // If we don't have at least memset and memcpy, there is little point of doing
   // anything here.  These are required by a freestanding implementation, so if
   // even they are disabled, there is no point in trying hard.
-  if (!TLI->has(LibFunc_memset) || !TLI->has(LibFunc_memcpy))
+  bool ShoudRunMemCpyOpt =
+      (TLI->has(LibFunc_memset) && TLI->has(LibFunc_memcpy))
+      // Some targets have libcalls disabled, but still want to run the pass.
+      // TODO: the pass should not depend on libcall availability as the targets
+      // should provide alternative ways of lowering standard LLVM
+      // intrinsics. Alas, there are existing users that can't currently handle
+      // `memset` intrinsic materialized by this pass.  See
+      // https://reviews.llvm.org/D104801 for the details.
+      || EnableMemCpyOptWithoutLibcalls;
+  if (!ShoudRunMemCpyOpt)
     return false;
 
   while (true) {
Index: clang/lib/Driver/ToolChains/Cuda.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Cuda.cpp
+++ clang/lib/Driver/ToolChains/Cuda.cpp
@@ -686,7 +686,8 @@
          "Only OpenMP or CUDA offloading kinds are supported for NVIDIA GPUs.");
 
   if (DeviceOffloadingKind == Action::OFK_Cuda) {
-    CC1Args.push_back("-fcuda-is-device");
+    CC1Args.append(
+        {"-fcuda-is-device", "-mllvm", "-enable-memcpyopt-without-libcalls"});
 
     if (DriverArgs.hasFlag(options::OPT_fcuda_approx_transcendentals,
                            options::OPT_fno_cuda_approx_transcendentals, false))


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