[MIPS] match llvm.{min,max}num with {min,max}.fmt for R6

- The behavior is similar to UCOMISD on x86, which is also used to
  compare two fp values, specifically on handling of NaNs.

Author: Cyanoxygen

llvm/lib/Target/Mips/MipsISelLowering.cpp

@@ -358,6 +358,15 @@ MipsTargetLowering::MipsTargetLowering(const MipsTargetMachine &TM,
   setOperationAction(ISD::FCOPYSIGN,          MVT::f64,   Custom);
   setOperationAction(ISD::FP_TO_SINT,         MVT::i32,   Custom);
 
+  // Lower fmin and fmax operations for MIPS R6.
+  // Instructions are defined but never used.
+  if (Subtarget.hasMips32r6()) {
+    setOperationAction(ISD::FMINNUM, MVT::f32, Legal);
+    setOperationAction(ISD::FMINNUM, MVT::f64, Legal);
+    setOperationAction(ISD::FMAXNUM, MVT::f32, Legal);
+    setOperationAction(ISD::FMAXNUM, MVT::f64, Legal);
+  }
+
   if (Subtarget.isGP64bit()) {
     setOperationAction(ISD::GlobalAddress,      MVT::i64,   Custom);
     setOperationAction(ISD::BlockAddress,       MVT::i64,   Custom);