Fix convertBFloatAPFloatToAPInt for NaN/Inf values

[dcaballe]

Summary

Bfloat type has an 8-bit exponent so the exponent of NaN/Inf numbers
must be 0xff instead of 0x1f. This is probably a copy-paste mistake
from the half float type.

[lattner]

nice catch

[stuij]

Ah, awesome. Thanks :)

llvm/lib/Support/APFloat.cpp

if (isFiniteNonZero()) {
     myexponent = exponent + 127; // bias
     mysignificand = (uint32_t)*significandParts();
     if (myexponent == 1 && !(mysignificand & 0x80))
       myexponent = 0; // denormal
   } else if (category == fcZero) {
     myexponent = 0;
     mysignificand = 0;
   } else if (category == fcInfinity) {
-    myexponent = 0x1f;
+    myexponent = 0xff;
     mysignificand = 0;
   } else {
     assert(category == fcNaN && "Unknown category!");
-    myexponent = 0x1f;
+    myexponent = 0xff;
     mysignificand = (uint32_t)*significandParts();
   }
 
   return APInt(16, (((sign & 1) << 15) | ((myexponent & 0xff) << 7) |
                     (mysignificand & 0x7f)));
 }
 
 APInt IEEEFloat::convertHalfAPFloatToAPInt() const {

llvm/test/Assembler/bfloat.ll

; OPT: 0xR4140
   ret bfloat %tmp
 }
 
 define float @check_bfloat_convert() {
   %tmp = fpext bfloat 0xR4C8D to float
 ; OPT: 0x4191A00000000000
   ret float %tmp
 }
+
+; ASSEM-DISASS-LABEL @snan_bfloat
+define bfloat @snan_bfloat() {
+; ASSEM-DISASS: ret bfloat 0xR7F81
+    ret bfloat 0xR7F81
+}
+
+; ASSEM-DISASS-LABEL @qnan_bfloat
+define bfloat @qnan_bfloat() {
+; ASSEM-DISASS: ret bfloat 0xR7FC0
+    ret bfloat 0xR7FC0
+}
+
+; ASSEM-DISASS-LABEL @pos_inf_bfloat
+define bfloat @pos_inf_bfloat() {
+; ASSEM-DISASS: ret bfloat 0xR7F80
+    ret bfloat 0xR7F80
+}
+
+; ASSEM-DISASS-LABEL @neg_inf_bfloat
+define bfloat @neg_inf_bfloat() {
+; ASSEM-DISASS: ret bfloat 0xRFF80
+    ret bfloat 0xRFF80
+}