Always honor fp-contract pragmas on PlayStation

The pragma:
    #pragma clang fp contract (off)

can be used to disable FMA, but when cross-statement FMA is enabled in
`fast` fp contract mode (via `-ffast-math`, for example), the effect of
that pragma is suppressed.

To have Clang honor that pragma in 'fast' fp contract mode in C/C++, an
additional switch:
    -ffp-contract=fast-honor-pragmas

must be applied.  On PlayStation, we want to always honor that pragma,
without requiring the additional switch to be specified.  This commit
does that.

Author: wjristow

clang/lib/CodeGen/BackendUtil.cpp

@@ -396,7 +396,11 @@ static bool initTargetOptions(const CompilerInstance &CI,
     Options.AllowFPOpFusion = llvm::FPOpFusion::Standard;
     break;
   case LangOptions::FPM_Fast:
-    Options.AllowFPOpFusion = llvm::FPOpFusion::Fast;
+    // We always honor fp-contract pragmas for PlayStation.
+    if (CI.getASTContext().getTargetInfo().getTriple().isPS())
+      Options.AllowFPOpFusion = llvm::FPOpFusion::Standard;
+    else
+      Options.AllowFPOpFusion = llvm::FPOpFusion::Fast;
     break;
   }
 

clang/test/CodeGen/X86/fma-fast-pragma.cpp

@@ -0,0 +1,53 @@
+// REQUIRES: x86-registered-target
+
+// With the pragma in place, generic targets leave FMA enabled unless the
+// switch '-ffp-contract=fast-honor-pragmas' is used to disable it; whereas
+// for PlayStation, the pragma is always honored, so FMA is disabled even in
+// plain 'fast' mode:
+// RUN: %clang_cc1 -S -triple x86_64-unknown-unknown -target-feature +fma \
+// RUN:   -O2 -ffp-contract=fast -o - %s | \
+// RUN:   FileCheck --check-prefix=CHECK-YES-FMA %s
+// RUN: %clang_cc1 -S -triple x86_64-unknown-unknown -target-feature +fma \
+// RUN:   -O2 -ffp-contract=fast-honor-pragmas -o - %s | \
+// RUN:   FileCheck --check-prefix=CHECK-NO-FMA %s
+// RUN: %clang_cc1 -S -triple x86_64-unknown-unknown -target-feature +fma \
+// RUN:   -O2 -ffp-contract=fast -ffp-contract=fast-honor-pragmas -o - %s | \
+// RUN:   FileCheck --check-prefix=CHECK-NO-FMA %s
+// RUN: %clang_cc1 -S -triple x86_64-sie-ps5 -target-feature +fma \
+// RUN:   -O2 -ffp-contract=fast -o - %s | \
+// RUN:   FileCheck --check-prefix=CHECK-NO-FMA %s
+// RUN: %clang_cc1 -S -triple x86_64-sie-ps5 -target-feature +fma \
+// RUN:   -O2 -ffp-contract=fast-honor-pragmas -o - %s | \
+// RUN:   FileCheck --check-prefix=CHECK-NO-FMA %s
+//
+// With the pragma suppressed, FMA happens in 'fast' or 'fast-honor-pragmas'
+// modes (for generic targets and for PlayStation):
+// RUN: %clang_cc1 -S -DSUPPRESS_PRAGMA \
+// RUN:   -triple x86_64-unknown-unknown -target-feature +fma \
+// RUN:   -O2 -ffp-contract=fast -o - %s | \
+// RUN:   FileCheck --check-prefix=CHECK-YES-FMA %s
+// RUN: %clang_cc1 -S -DSUPPRESS_PRAGMA \
+// RUN:   -triple x86_64-unknown-unknown -target-feature +fma \
+// RUN:   -O2 -ffp-contract=fast-honor-pragmas -o - %s | \
+// RUN:   FileCheck --check-prefix=CHECK-YES-FMA %s
+// RUN: %clang_cc1 -S -DSUPPRESS_PRAGMA \
+// RUN:   -triple x86_64-sie-ps5 -target-feature +fma \
+// RUN:   -O2 -ffp-contract=fast -o - %s | \
+// RUN:   FileCheck --check-prefix=CHECK-YES-FMA %s
+// RUN: %clang_cc1 -S -DSUPPRESS_PRAGMA \
+// RUN:   -triple x86_64-sie-ps5 -target-feature +fma \
+// RUN:   -O2 -ffp-contract=fast-honor-pragmas -o - %s | \
+// RUN:   FileCheck --check-prefix=CHECK-YES-FMA %s
+//
+float compute(float a, float b, float c) {
+#if !defined(SUPPRESS_PRAGMA)
+#pragma clang fp contract (off)
+#endif
+  float product = a * b;
+  return product + c;
+}
+
+// CHECK-NO-FMA: vmulss
+// CHECK-NO-FMA-NEXT: vaddss
+
+// CHECK-YES-FMA: vfmadd213ss