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"MOffset" size estimate fix #63766

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Merged
jakobbotsch merged 1 commit into from
Jan 15, 2022
Merged

"MOffset" size estimate fix #63766

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13 changes: 13 additions & 0 deletions src/coreclr/jit/emitxarch.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2565,6 +2565,19 @@ UNATIVE_OFFSET emitter::emitInsSizeAM(instrDesc* id, code_t code)
if (reg == REG_NA)
{
/* The address is of the form "[disp]" */
CLANG_FORMAT_COMMENT_ANCHOR;

#ifdef TARGET_X86
// Special case: "mov eax, [disp]" and "mov [disp], eax" can use a smaller 1-byte encoding.
if ((ins == INS_mov) && (id->idReg1() == REG_EAX) &&
((id->idInsFmt() == IF_RWR_ARD) || (id->idInsFmt() == IF_AWR_RRD)))
{
// Amd64: this is one case where addr can be 64-bit in size. This is currently unused.
// If this ever changes, this code will need to be updated to add "sizeof(INT64)" to "size".
assert((size == 2) || ((size == 3) && (id->idOpSize() == EA_2BYTE)));
size--;
}
#endif

size += sizeof(INT32);

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