[SYCL][Driver] Propagate floating point optimizations flag (#2680)

SPIR-V compiler(s) support `-cl-fast-relaxed-math` option enabling a set
of optimizations over floating point values. This change maps Clang's
`-ffast-math`, `-Ofast`, `-ffp-model=fast` and `-funsafe-math-optimizations` 
to this SPIR-V compiler option.

Author: bader

clang/lib/Driver/ToolChains/SYCL.cpp

@@ -511,6 +511,19 @@ static void addImpliedArgs(const llvm::Triple &Triple,
       BeArgs.push_back("-g");
   if (Args.getLastArg(options::OPT_O0))
     BeArgs.push_back("-cl-opt-disable");
+  // Check if floating pointing optimizations are allowed.
+  bool isFastMath = isOptimizationLevelFast(Args);
+  Arg *A = Args.getLastArg(options::OPT_ffast_math, options::OPT_fno_fast_math,
+                           options::OPT_funsafe_math_optimizations,
+                           options::OPT_fno_unsafe_math_optimizations);
+  isFastMath =
+      isFastMath || (A && (A->getOption().getID() == options::OPT_ffast_math ||
+                           A->getOption().getID() ==
+                               options::OPT_funsafe_math_optimizations));
+  A = Args.getLastArg(options::OPT_ffp_model_EQ);
+  isFastMath = isFastMath || (A && StringRef(A->getValue()).equals("fast"));
+  if (isFastMath)
+    BeArgs.push_back("-cl-fast-relaxed-math");
   if (BeArgs.empty())
     return;
   if (Triple.getSubArch() == llvm::Triple::NoSubArch ||

clang/test/Driver/sycl-offload.c

@@ -904,5 +904,13 @@
 // CHECK-STD-OVR: clang{{.*}} "-emit-obj" {{.*}} "-std=c++14"
 // CHECK-STD-OVR-NOT: clang{{.*}} "-std=c++17"
 
+// Bypass -cl-fast-relaxed-math to SPIR-V compiler.
+// RUN: %clang -### -fsycl -fsycl-targets=spir64-unknown-unknown-sycldevice -ffast-math %s 2>&1 | FileCheck -check-prefix=CHECK-FAST-MATH-OPT %s
+// RUN: %clang -### -fsycl -fsycl-targets=spir64-unknown-unknown-sycldevice -funsafe-math-optimizations %s 2>&1 | FileCheck -check-prefix=CHECK-FAST-MATH-OPT %s
+// RUN: %clang -### -fsycl -fsycl-targets=spir64-unknown-unknown-sycldevice -Ofast %s 2>&1 | FileCheck -check-prefix=CHECK-FAST-MATH-OPT %s
+// RUN: %clang -### -fsycl -fsycl-targets=spir64-unknown-unknown-sycldevice -ffp-model=fast %s 2>&1 | FileCheck -check-prefix=CHECK-FAST-MATH-OPT %s
+// RUN: %clang_cl -### -fsycl -fsycl-targets=spir64-unknown-unknown-sycldevice /fp:fast %s 2>&1 | FileCheck -check-prefix=CHECK-FAST-MATH-OPT %s
+// CHECK-FAST-MATH-OPT: clang-offload-wrapper{{.*}} "-compile-opts=-cl-fast-relaxed-math"
+
 // TODO: SYCL specific fail - analyze and enable
 // XFAIL: windows-msvc