[RISCV] Correctly report sizes for builtin fixups

This is a different approach to fixing the problem described in D46746. 
RISCVAsmBackend currently depends on the getSize helper function returning the 
number of bytes a fixup may change (note: some other backends have a similar 
helper named getFixupNumKindBytes). As noted in that review, this doesn't 
return the correct size for FK_Data_1, FK_Data_2, or FK_Data_8 meaning that 
too few bytes will be written in the case of FK_Data_8, and there's the 
potential of writing outside the Data array for the smaller fixups.

D46746 extends getSize to recognise some of the builtin fixup types. Rather 
than having a function that needs to be kept up to date as new builtin or 
target-specific fixups are added, We can calculate an appropriate bound on the 
number of bytes that might be touched using Info.TargetSize and 
Info.TargetOffset.

Differential Revision: https://reviews.llvm.org/D46965

llvm-svn: 333076

llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.cpp

@@ -296,16 +296,6 @@ static uint64_t adjustFixupValue(const MCFixup &Fixup, uint64_t Value,
   }
 }
 
-static unsigned getSize(unsigned Kind) {
-  switch (Kind) {
-  default:
-    return 4;
-  case RISCV::fixup_riscv_rvc_jump:
-  case RISCV::fixup_riscv_rvc_branch:
-    return 2;
-  }
-}
-
 void RISCVAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                                  const MCValue &Target,
                                  MutableArrayRef<char> Data, uint64_t Value,
@@ -321,16 +311,13 @@ void RISCVAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
   Value <<= Info.TargetOffset;
 
   unsigned Offset = Fixup.getOffset();
-  unsigned FullSize = getSize(Fixup.getKind());
+  unsigned NumBytes = alignTo(Info.TargetSize + Info.TargetOffset, 8) / 8;
 
-#ifndef NDEBUG
-  unsigned NumBytes = (Info.TargetSize + 7) / 8;
   assert(Offset + NumBytes <= Data.size() && "Invalid fixup offset!");
-#endif
 
   // For each byte of the fragment that the fixup touches, mask in the
   // bits from the fixup value.
-  for (unsigned i = 0; i != FullSize; ++i) {
+  for (unsigned i = 0; i != NumBytes; ++i) {
     Data[Offset + i] |= uint8_t((Value >> (i * 8)) & 0xff);
   }
 }