[llvm] Ensure that soft float targets don't emit fma() libcalls. (#106615)

The previous behavior could be harmful in some edge cases, such as
emitting a call to `fma()` in the `fma()` implementation itself.

Do this by just being more accurate in `isFMAFasterThanFMulAndFAdd()`.
This was already done for PowerPC; this commit just extends that to Arm,
z/Arch, and x86. MIPS and SPARC already got it right, but I added tests
for them too, for good measure.

Note: I don't have commit access.

Author: alexrp

llvm/include/llvm/CodeGen/TargetLowering.h

@@ -3223,6 +3223,9 @@ class TargetLoweringBase {
   /// not legal, but should return true if those types will eventually legalize
   /// to types that support FMAs. After legalization, it will only be called on
   /// types that support FMAs (via Legal or Custom actions)
+  ///
+  /// Targets that care about soft float support should return false when soft
+  /// float code is being generated (i.e. use-soft-float).
   virtual bool isFMAFasterThanFMulAndFAdd(const MachineFunction &MF,
                                           EVT) const {
     return false;

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -19354,6 +19354,9 @@ bool ARMTargetLowering::allowTruncateForTailCall(Type *Ty1, Type *Ty2) const {
 /// patterns (and we don't have the non-fused floating point instruction).
 bool ARMTargetLowering::isFMAFasterThanFMulAndFAdd(const MachineFunction &MF,
                                                    EVT VT) const {
+  if (Subtarget->useSoftFloat())
+    return false;
+
   if (!VT.isSimple())
     return false;
 

llvm/lib/Target/SystemZ/SystemZISelLowering.cpp

@@ -793,6 +793,9 @@ EVT SystemZTargetLowering::getSetCCResultType(const DataLayout &DL,
 
 bool SystemZTargetLowering::isFMAFasterThanFMulAndFAdd(
     const MachineFunction &MF, EVT VT) const {
+  if (useSoftFloat())
+    return false;
+
   VT = VT.getScalarType();
 
   if (!VT.isSimple())

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -34838,6 +34838,9 @@ bool X86TargetLowering::isVectorLoadExtDesirable(SDValue ExtVal) const {
 
 bool X86TargetLowering::isFMAFasterThanFMulAndFAdd(const MachineFunction &MF,
                                                    EVT VT) const {
+  if (Subtarget.useSoftFloat())
+    return false;
+
   if (!Subtarget.hasAnyFMA())
     return false;