[CUDA] Enable fusing FP ops (-ffp-contract=fast) for CUDA by default.

This matches default nvcc behavior and gives substantial
performance boost on GPU where fmad is much cheaper compared to add+mul.

Differential Revision: http://reviews.llvm.org/D20341

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@270094 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 7c3850eeabe8a334cc677f9295e1c50078254ac6..c5f839e67374394bd57c50cf86057ab9f11edf95 100644 (file)
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -2255,10 +2255,15 @@ bool CompilerInvocation::CreateFromArgs(CompilerInvocation &Res,
       LangOpts.ObjCExceptions = 1;
   }
 
-  // During CUDA device-side compilation, the aux triple is the triple used for
-  // host compilation.
-  if (LangOpts.CUDA && LangOpts.CUDAIsDevice) {
-    Res.getTargetOpts().HostTriple = Res.getFrontendOpts().AuxTriple;
+  if (LangOpts.CUDA) {
+    // During CUDA device-side compilation, the aux triple is the
+    // triple used for host compilation.
+    if (LangOpts.CUDAIsDevice)
+      Res.getTargetOpts().HostTriple = Res.getFrontendOpts().AuxTriple;
+
+    // Set default FP_CONTRACT to FAST.
+    if (!Args.hasArg(OPT_ffp_contract))
+      Res.getCodeGenOpts().setFPContractMode(CodeGenOptions::FPC_Fast);
   }
 
   // FIXME: Override value name discarding when asan or msan is used because the

diff --git a/test/CodeGenCUDA/fp-contract.cu b/test/CodeGenCUDA/fp-contract.cu
new file mode 100644 (file)
index 0000000..070ebae
--- /dev/null
+++ b/test/CodeGenCUDA/fp-contract.cu
@@ -0,0 +1,32 @@
+// REQUIRES: x86-registered-target
+// REQUIRES: nvptx-registered-target
+
+// By default we should fuse multiply/add into fma instruction.
+// RUN: %clang_cc1 -fcuda-is-device -triple nvptx-nvidia-cuda -S \
+// RUN:   -disable-llvm-passes -o - %s | FileCheck -check-prefix ENABLED %s
+
+// Explicit -ffp-contract=fast
+// RUN: %clang_cc1 -fcuda-is-device -triple nvptx-nvidia-cuda -S \
+// RUN:   -ffp-contract=fast -disable-llvm-passes -o - %s \
+// RUN:   | FileCheck -check-prefix ENABLED %s
+
+// Explicit -ffp-contract=on -- fusing by front-end (disabled).
+// RUN: %clang_cc1 -fcuda-is-device -triple nvptx-nvidia-cuda -S \
+// RUN:   -ffp-contract=on -disable-llvm-passes -o - %s \
+// RUN:   | FileCheck -check-prefix DISABLED %s
+
+// Explicit -ffp-contract=off should disable instruction fusing.
+// RUN: %clang_cc1 -fcuda-is-device -triple nvptx-nvidia-cuda -S \
+// RUN:   -ffp-contract=off -disable-llvm-passes -o - %s \
+// RUN:   | FileCheck -check-prefix DISABLED %s
+
+
+#include "Inputs/cuda.h"
+
+__host__ __device__ float func(float a, float b, float c) { return a + b * c; }
+// ENABLED:       fma.rn.f32
+// ENABLED-NEXT:  st.param.f32
+
+// DISABLED:      mul.rn.f32
+// DISABLED-NEXT: add.rn.f32
+// DISABLED-NEXT: st.param.f32