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tcg-i386: Remove "cb" output restriction from qemu_st8 for i386 

Once we form a combined qemu_st_i32 opcode, we won't be able to
have separate constraints based on size.  This one is fairly easy
to work around, since eax is available as a scratch register.

When storing variable data, this tends to merely exchange one mov
for another.  E.g.

-:  mov    %esi,%ecx
...
-:  mov    %cl,(%edx)
+:  mov    %esi,%eax
+:  mov    %al,(%edx)

Where we do have a regression is when storing constant data, in which
we may load the constant into edi, when only ecx/ebx ought to be used.

The proper way to recover this regression is to allow constants as
arguments to qemu_st_i32, so that we never load the constant data into
a register at all, must less the wrong register.  TBD.

Signed-off-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Richard Henderson 2013-09-04 08:51:07 -07:00
parent 7352ee546c
commit b3e2bc500f
1 changed files with 8 additions and 2 deletions
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10
tcg/i386/tcg-target.c
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@ -1479,6 +1479,12 @@ static void tcg_out_qemu_st_direct(TCGContext *s, TCGReg datalo, TCGReg datahi,
switch (memop & MO_SIZE) {
case MO_8:
/* In 32-bit mode, 8-byte stores can only happen from [abcd]x.
Use the scratch register if necessary. */
if (TCG_TARGET_REG_BITS == 32 && datalo >= 4) {
tcg_out_mov(s, TCG_TYPE_I32, scratch, datalo);
datalo = scratch;
}
tcg_out_modrm_offset(s, OPC_MOVB_EvGv + P_REXB_R + seg,
datalo, base, ofs);
break;
@ -2084,7 +2090,7 @@ static const TCGTargetOpDef x86_op_defs[] = {
{ INDEX_op_qemu_ld32, { "r", "L" } },
{ INDEX_op_qemu_ld64, { "r", "r", "L" } },
{ INDEX_op_qemu_st8, { "cb", "L" } },
{ INDEX_op_qemu_st8, { "L", "L" } },
{ INDEX_op_qemu_st16, { "L", "L" } },
{ INDEX_op_qemu_st32, { "L", "L" } },
{ INDEX_op_qemu_st64, { "L", "L", "L" } },
@ -2096,7 +2102,7 @@ static const TCGTargetOpDef x86_op_defs[] = {
{ INDEX_op_qemu_ld32, { "r", "L", "L" } },
{ INDEX_op_qemu_ld64, { "r", "r", "L", "L" } },
{ INDEX_op_qemu_st8, { "cb", "L", "L" } },
{ INDEX_op_qemu_st8, { "L", "L", "L" } },
{ INDEX_op_qemu_st16, { "L", "L", "L" } },
{ INDEX_op_qemu_st32, { "L", "L", "L" } },
{ INDEX_op_qemu_st64, { "L", "L", "L", "L" } },