Set some fast math attributes in setFunctionAttributes

This will provide a more consistent view to codegen for these
attributes. The current system is somewhat awkward, and the fields in
TargetOptions are reset based on the command line flag if the
attribute isn't set. By forcing these attributes with the flag, there
can never be an inconsistency in the behavior if code directly
inspects the attribute on the function without considering the command
line flags.

Author: arsenm

llvm/include/llvm/CodeGen/CommandFlags.inc

@@ -377,6 +377,17 @@ LLVM_ATTRIBUTE_UNUSED static std::vector<std::string> getFeatureList() {
   return Features.getFeatures();
 }
 
+static void renderBoolStringAttr(AttrBuilder &B, StringRef Name, bool Val) {
+  B.addAttribute(Name, Val ? "true" : "false");
+}
+
+#define HANDLE_BOOL_ATTR(CL, AttrName)                              \
+  do {                                                              \
+    if (CL.getNumOccurrences() > 0 && !F.hasFnAttribute(AttrName))  \
+      renderBoolStringAttr(NewAttrs, AttrName, CL);                 \
+  } while (0)
+
+
 /// Set function attributes of function \p F based on CPU, Features, and command
 /// line flags.
 LLVM_ATTRIBUTE_UNUSED static void
@@ -415,6 +426,11 @@ setFunctionAttributes(StringRef CPU, StringRef Features, Function &F) {
   if (StackRealign)
     NewAttrs.addAttribute("stackrealign");
 
+  HANDLE_BOOL_ATTR(EnableUnsafeFPMath, "unsafe-fp-math");
+  HANDLE_BOOL_ATTR(EnableNoInfsFPMath, "no-infs-fp-math");
+  HANDLE_BOOL_ATTR(EnableNoNaNsFPMath, "no-nans-fp-math");
+  HANDLE_BOOL_ATTR(EnableNoSignedZerosFPMath, "no-signed-zeros-fp-math");
+
   if (TrapFuncName.getNumOccurrences() > 0)
     for (auto &B : F)
       for (auto &I : B)

llvm/lib/Target/TargetMachine.cpp

@@ -46,17 +46,17 @@ bool TargetMachine::isPositionIndependent() const {
 }
 
 /// Reset the target options based on the function's attributes.
+/// setFunctionAttributes should have made the raw attribute value consistent
+/// with the command line flag if used.
+//
 // FIXME: This function needs to go away for a number of reasons:
 // a) global state on the TargetMachine is terrible in general,
 // b) these target options should be passed only on the function
 //    and not on the TargetMachine (via TargetOptions) at all.
 void TargetMachine::resetTargetOptions(const Function &F) const {
-#define RESET_OPTION(X, Y)                                                     \
-  do {                                                                         \
-    if (F.hasFnAttribute(Y))                                                   \
-      Options.X = (F.getFnAttribute(Y).getValueAsString() == "true");          \
-    else                                                                       \
-      Options.X = DefaultOptions.X;                                            \
+#define RESET_OPTION(X, Y)                                              \
+  do {                                                                  \
+    Options.X = (F.getFnAttribute(Y).getValueAsString() == "true");     \
   } while (0)
 
   RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");