[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.
- Update related tests regarding this change.

Author: Cyanoxygen

llvm/lib/Target/Mips/Mips32r6InstrInfo.td

@@ -1117,6 +1117,22 @@ def : MipsPat<(select i32:$cond, immz, i32:$f),
               ISA_MIPS32R6;
 }
 
+// llvm.fmin/fmax operations.
+let AdditionalPredicates = [NotInMicroMips] in {
+  def : MipsPat<(fmaxnum f32:$lhs, f32:$rhs),
+                (MAX_S   f32:$lhs, f32:$rhs)>,
+                ISA_MIPS32R6;
+  def : MipsPat<(fmaxnum f64:$lhs, f64:$rhs),
+                (MAX_D   f64:$lhs, f64:$rhs)>,
+                ISA_MIPS32R6;
+  def : MipsPat<(fminnum f32:$lhs, f32:$rhs),
+                (MIN_S   f32:$lhs, f32:$rhs)>,
+                ISA_MIPS32R6;
+  def : MipsPat<(fminnum f64:$lhs, f64:$rhs),
+                (MIN_D   f64:$lhs, f64:$rhs)>,
+                ISA_MIPS32R6;
+}
+
 // Pseudo instructions
 let isCall = 1, isTerminator = 1, isReturn = 1, isBarrier = 1, hasDelaySlot = 1,
     hasExtraSrcRegAllocReq = 1, isCTI = 1, Defs = [AT], hasPostISelHook = 1 in {

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);