[ExpandLargeFpConvert] Support bfloat. (#87619)

The conversion expansions did not properly handle bfloat types.

I'm not certain that these expansions are completely correct;
I don't have any experience with AMDGPU or the ability to run
anything to test it.

Note that it doesn't seem like AMDGPU with GlobalISel can
handle fptrunc of float to bfloat, which is needed for itofp.
I've omitted the GISEL run for the bfloat case.

This fixes #85379.

llvm/lib/CodeGen/ExpandLargeFpConvert.cpp

@@ -116,7 +116,8 @@ static void expandFPToI(Instruction *FPToI) {
   // fp80 conversion is implemented by fpext to fp128 first then do the
   // conversion.
   FPMantissaWidth = FPMantissaWidth == 63 ? 112 : FPMantissaWidth;
-  unsigned FloatWidth = PowerOf2Ceil(FPMantissaWidth);
+  unsigned FloatWidth =
+      PowerOf2Ceil(FloatVal->getType()->getScalarSizeInBits());
   unsigned ExponentWidth = FloatWidth - FPMantissaWidth - 1;
   unsigned ExponentBias = (1 << (ExponentWidth - 1)) - 1;
   Value *ImplicitBit = Builder.CreateShl(
@@ -319,6 +320,7 @@ static void expandIToFP(Instruction *IToFP) {
   // FIXME: As there is no related builtins added in compliler-rt,
   // here currently utilized the fp32 <-> fp16 lib calls to implement.
   FPMantissaWidth = FPMantissaWidth == 10 ? 23 : FPMantissaWidth;
+  FPMantissaWidth = FPMantissaWidth == 7 ? 23 : FPMantissaWidth;
   unsigned FloatWidth = PowerOf2Ceil(FPMantissaWidth);
   bool IsSigned = IToFP->getOpcode() == Instruction::SIToFP;
 
@@ -547,7 +549,7 @@ static void expandIToFP(Instruction *IToFP) {
     Value *A40 =
         Builder.CreateBitCast(Or35, Type::getFP128Ty(Builder.getContext()));
     A4 = Builder.CreateFPTrunc(A40, IToFP->getType());
-  } else if (IToFP->getType()->isHalfTy()) {
+  } else if (IToFP->getType()->isHalfTy() || IToFP->getType()->isBFloatTy()) {
     // Deal with "half" situation. This is a workaround since we don't have
     // floattihf.c currently as referring.
     Value *A40 =