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cmd/compile: rethink temporary names #7923

josharian opened this issue May 2, 2014 · 5 comments

cmd/compile: rethink temporary names #7923

josharian opened this issue May 2, 2014 · 5 comments


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package p

func conv() {
    var f float64
    _ = float64(uint64(f))

go version devel +b0443478e712 Thu May 01 16:29:34 2014 -0400 darwin/386

go tool 8g -S conv.go

The assembly listing includes:

    0x00b7 00183 (conv.go:5)    FMOVDP  F0,"".autotmp_0001+20(SP)
    0x00bb 00187 (conv.go:5)    JMP ,130
    0x00bd 00189 (conv.go:5)    FSTCW   ,""..utotmp_0004+2(SP)
    0x00c1 00193 (conv.go:5)    MOVW    $3967,""..utotmp_0005+0(SP)
    0x00c7 00199 (conv.go:5)    FLDCW   ""..utotmp_0005+0(SP),
    0x00ca 00202 (conv.go:5)    FMOVD   $f64.43e0000000000000+0(SB),F0
    0x00d0 00208 (conv.go:5)    FUCOMIP F0,F1
    0x00d2 00210 (conv.go:5)    JLS ,225
    0x00d4 00212 (conv.go:5)    FMOVVP  F0,"".autotmp_0003+12(SP)
    0x00d8 00216 (conv.go:5)    FLDCW   ""..utotmp_0004+2(SP),

Note the variable names ""..utotmp_0004 and ""..utotmp_0005. There
is downstream code that checks for the "autotmp" prefix, so this name
corruption is potentially significant. Not all autotmp names are corrupted (see

I've not seen name corruption with either 5g or 6g.
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Contributor Author

Comment 1:

Urk. Actually, it looks like this is done intentionally in memname (8g/gsubr.c):
    namebuf[0] = '.';   // keep optimizer from registerizing
The question is now: Is this safe, given the downstream users of this information? I see
at least two non-optimizer clients of the "autotmp" name -- racewalk and dwarf

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Comment 3:

Labels changed: added repo-main, release-go1.3maybe.

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rsc commented May 12, 2014

Comment 4:

racewalk and dwarf both seem to be working okay.
I would like to change these names, though. In particular I'd like to use the shorter
construct '%c.%d' where the first character can vary according to the kind of name. t.%d
for most temps, m.%d for these memory temps in 8g, maybe p.%d for the parameter shadow
variables, maybe something different for order.c-introduced temps vs others (because the
former are cleaned up better).
But that can't happen until 1.4.

Labels changed: added release-go1.4, removed release-go1.3maybe.

Status changed to Accepted.

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rsc commented Sep 24, 2014

Comment 5:

Labels changed: added release-go1.5, removed release-go1.4.

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rsc commented May 19, 2015

We can rethink what's left of this once Keith is done with SSA.

@rsc rsc modified the milestones: Unplanned, Go1.5 May 19, 2015
@rsc rsc changed the title cmd/gc: rethink temporary names cmd/compile: rethink temporary names Jun 8, 2015
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