[AMDGPU] Add option -munsafe-fp-atomics

Add an option -munsafe-fp-atomics for AMDGPU target.

When enabled, clang adds function attribute "amdgpu-unsafe-fp-atomics"
to any functions for amdgpu target. This allows amdgpu backend to use
unsafe fp atomic instructions in these functions.

Differential Revision: https://reviews.llvm.org/D91546

clang/include/clang/Basic/TargetInfo.h

@@ -218,6 +218,8 @@ class TargetInfo : public virtual TransferrableTargetInfo,
 
   unsigned HasAArch64SVETypes : 1;
 
+  unsigned AllowAMDGPUUnsafeFPAtomics : 1;
+
   unsigned ARMCDECoprocMask : 8;
 
   unsigned MaxOpenCLWorkGroupSize;
@@ -857,6 +859,10 @@ class TargetInfo : public virtual TransferrableTargetInfo,
   /// available on this target.
   bool hasAArch64SVETypes() const { return HasAArch64SVETypes; }
 
+  /// Returns whether or not the AMDGPU unsafe floating point atomics are
+  /// allowed.
+  bool allowAMDGPUUnsafeFPAtomics() const { return AllowAMDGPUUnsafeFPAtomics; }
+
   /// For ARM targets returns a mask defining which coprocessors are configured
   /// as Custom Datapath.
   uint32_t getARMCDECoprocMask() const { return ARMCDECoprocMask; }

clang/include/clang/Basic/TargetOptions.h

@@ -75,6 +75,9 @@ class TargetOptions {
   /// address space.
   bool NVPTXUseShortPointers = false;
 
+  /// \brief If enabled, allow AMDGPU unsafe floating point atomics.
+  bool AllowAMDGPUUnsafeFPAtomics = false;
+
   // The code model to be used as specified by the user. Corresponds to
   // CodeModel::Model enum defined in include/llvm/Support/CodeGen.h, plus
   // "default" for the case when the user has not explicitly specified a

clang/include/clang/Driver/Options.td

@@ -2546,6 +2546,11 @@ def mxnack : Flag<["-"], "mxnack">, Group<m_amdgpu_Features_Group>,
   HelpText<"Specify XNACK mode (AMDGPU only)">;
 def mno_xnack : Flag<["-"], "mno-xnack">, Group<m_amdgpu_Features_Group>;
 
+def munsafe_fp_atomics : Flag<["-"], "munsafe-fp-atomics">, Group<m_Group>,
+  HelpText<"Enable unsafe floating point atomic instructions (AMDGPU only)">,
+  Flags<[CC1Option]>;
+def mno_unsafe_fp_atomics : Flag<["-"], "mno-unsafe-fp-atomics">, Group<m_Group>;
+
 def faltivec : Flag<["-"], "faltivec">, Group<f_Group>, Flags<[NoXarchOption]>;
 def fno_altivec : Flag<["-"], "fno-altivec">, Group<f_Group>, Flags<[NoXarchOption]>;
 def maltivec : Flag<["-"], "maltivec">, Group<m_ppc_Features_Group>;

clang/lib/Basic/TargetInfo.cpp

@@ -115,6 +115,7 @@ TargetInfo::TargetInfo(const llvm::Triple &T) : TargetOpts(), Triple(T) {
   HasBuiltinMSVaList = false;
   IsRenderScriptTarget = false;
   HasAArch64SVETypes = false;
+  AllowAMDGPUUnsafeFPAtomics = false;
   ARMCDECoprocMask = 0;
 
   // Default to no types using fpret.

clang/lib/Basic/Targets/AMDGPU.cpp

@@ -323,6 +323,7 @@ AMDGPUTargetInfo::AMDGPUTargetInfo(const llvm::Triple &Triple,
   HasLegalHalfType = true;
   HasFloat16 = true;
   WavefrontSize = GPUFeatures & llvm::AMDGPU::FEATURE_WAVE32 ? 32 : 64;
+  AllowAMDGPUUnsafeFPAtomics = Opts.AllowAMDGPUUnsafeFPAtomics;
 
   // Set pointer width and alignment for target address space 0.
   PointerWidth = PointerAlign = DataLayout->getPointerSizeInBits();

clang/lib/CodeGen/TargetInfo.cpp

@@ -9080,6 +9080,9 @@ void AMDGPUTargetCodeGenInfo::setTargetAttributes(
     if (NumVGPR != 0)
       F->addFnAttr("amdgpu-num-vgpr", llvm::utostr(NumVGPR));
   }
+
+  if (M.getContext().getTargetInfo().allowAMDGPUUnsafeFPAtomics())
+    F->addFnAttr("amdgpu-unsafe-fp-atomics", "true");
 }
 
 unsigned AMDGPUTargetCodeGenInfo::getOpenCLKernelCallingConv() const {

clang/lib/Driver/ToolChains/Clang.cpp

@@ -6217,6 +6217,11 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   }
 
   HandleAmdgcnLegacyOptions(D, Args, CmdArgs);
+  if (Triple.isAMDGPU()) {
+    if (Args.hasFlag(options::OPT_munsafe_fp_atomics,
+                     options::OPT_mno_unsafe_fp_atomics))
+      CmdArgs.push_back("-munsafe-fp-atomics");
+  }
 
   // For all the host OpenMP offloading compile jobs we need to pass the targets
   // information using -fopenmp-targets= option.

clang/lib/Frontend/CompilerInvocation.cpp

@@ -3747,6 +3747,9 @@ static void ParseTargetArgs(TargetOptions &Opts, ArgList &Args,
   Opts.ForceEnableInt128 = Args.hasArg(OPT_fforce_enable_int128);
   Opts.NVPTXUseShortPointers = Args.hasFlag(
       options::OPT_fcuda_short_ptr, options::OPT_fno_cuda_short_ptr, false);
+  Opts.AllowAMDGPUUnsafeFPAtomics =
+      Args.hasFlag(options::OPT_munsafe_fp_atomics,
+                   options::OPT_mno_unsafe_fp_atomics, false);
   if (Arg *A = Args.getLastArg(options::OPT_target_sdk_version_EQ)) {
     llvm::VersionTuple Version;
     if (Version.tryParse(A->getValue()))

clang/test/CodeGenCUDA/amdgpu-func-attrs.cu

@@ -0,0 +1,22 @@
+// RUN: %clang_cc1 -triple amdgcn-amd-amdhsa \
+// RUN:     -fcuda-is-device -emit-llvm -o - -x hip %s \
+// RUN:     | FileCheck -check-prefixes=NO-UNSAFE-FP-ATOMICS %s
+// RUN: %clang_cc1 -triple amdgcn-amd-amdhsa \
+// RUN:     -fcuda-is-device -emit-llvm -o - -x hip %s \
+// RUN:     -munsafe-fp-atomics \
+// RUN:     | FileCheck -check-prefixes=UNSAFE-FP-ATOMICS %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm \
+// RUN:     -o - -x hip %s -munsafe-fp-atomics \
+// RUN:     | FileCheck -check-prefix=NO-UNSAFE-FP-ATOMICS %s
+
+#include "Inputs/cuda.h"
+
+__device__ void test() {
+// UNSAFE-FP-ATOMICS: define void @_Z4testv() [[ATTR:#[0-9]+]]
+}
+
+
+// Make sure this is silently accepted on other targets.
+// NO-UNSAFE-FP-ATOMICS-NOT: "amdgpu-unsafe-fp-atomics"
+
+// UNSAFE-FP-ATOMICS-DAG: attributes [[ATTR]] = {{.*}}"amdgpu-unsafe-fp-atomics"="true"

clang/test/Driver/hip-options.hip

@@ -31,3 +31,7 @@
 // HOST-NOT: clang{{.*}} "-fcuda-is-device" {{.*}} "-debug-info-kind={{.*}}"
 // HOST-NOT: clang{{.*}} "-fcuda-is-device" {{.*}} "-debug-info-kind={{.*}}"
 // HOST: clang{{.*}} "-debug-info-kind={{.*}}"
+
+// RUN: %clang -### -nogpuinc -nogpulib -munsafe-fp-atomics \
+// RUN:   --cuda-gpu-arch=gfx906  %s 2>&1 | FileCheck -check-prefix=UNSAFE-FP-ATOMICS %s
+// UNSAFE-FP-ATOMICS: clang{{.*}} "-triple" "amdgcn-amd-amdhsa" {{.*}} "-munsafe-fp-atomics"