https://issues.dlang.org/show_bug.cgi?id=12833
yebblies <yebbl...@gmail.com> changed:
What |Removed |Added
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CC| |bugzi...@digitalmars.com,
| |yebbl...@gmail.com
--- Comment #2 from yebblies <yebbl...@gmail.com> ---
So, the problem is:
1. the code is emitted to bitwise and a long with 0xFFFF (and EAX with 0xFFFF,
and EDX with 0x0)
2. the compiler checks and decides to do nothing for the long -> ushort
conversion because the result is already in AX where it should be.
3. the zext code has a really dodgy check (cdshtlng cod4.c:2905) that promotes
(r16 & mask16) into (r32 & mask32), but doesn't bother checking that it's
actually anding the correct register - in this case it sees the "and EDX, 0"
and does nothing. It also sets the return register to whatever that
instruction was using and as a result later code-gen stupidly uses edx.
Making this change appears to fix it by disallowing the 'optimization' if the
register is wrong:
@@ -2900,11 +2900,11 @@ code *cdshtlng(elem *e,regm_t *pretregs)
c1 = codelem(e1,&retregs,FALSE);
c2 = getregs(retregs);
if (op == OPu16_32 && c1)
{
code *cx = code_last(c1);
- if (cx->Iop == 0x81 && (cx->Irm & modregrm(3,7,0)) ==
modregrm(3,4,0))
+ if (cx->Iop == 0x81 && (cx->Irm & modregrm(3,7,0)) ==
modregrm(3,4,0) && (1 << (cx->Irm & modregrm(0,0,7))) == retregs)
{
// Convert AND of a word to AND of a dword, zeroing upper word
retregs = mask[cx->Irm & 7];
if (cx->Irex & REX_B)
retregs = mask[8 | (cx->Irm & 7)];
Hopefully Walter can comment on the correctness of this patch.
--
