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reuse previous address constants in fold()

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parseref() has code to reuse address constants, but this is not
done in other passes such as fold or isel. Introduce a new function
newcon() which takes a Con and returns a Ref for that constant, and
use this whenever creating address constants.

This is necessary to fix folding of address constants when one
operand is already folded. For example, in

	%a =l add $x, 1
	%b =l add %a, 2
	%c =w loadw %b

%a and %b were folded to $x+1 and $x+3 respectively, but then the
second add is visited again since it uses %a. This gets folded to
$x+3 as well, but as a new distinct constant. This results in %b
getting labeled as bottom instead of either constant, disabling the
replacement of %b by a constant in subsequent instructions (such
as the loadw).
This commit is contained in:
Michael Forney 2021-11-18 01:45:27 -08:00 • committed by Quentin Carbonneaux
parent b0f16dad64
commit bf153b359e
6 changed files with 33 additions and 31 deletions
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7
amd64/isel.c
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@ -117,12 +117,9 @@ fixarg(Ref *r, int k, Ins *i, Fn *fn)
m = &fn->mem[r0.val];
if (req(m->base, R))
if (m->offset.type == CAddr) {
n = fn->ncon;
vgrow(&fn->con, ++fn->ncon);
fn->con[n] = m->offset;
m->offset.type = CUndef;
r0 = newtmp("isel", Kl, fn);
emit(Oaddr, Kl, r0, CON(n), R);
emit(Oaddr, Kl, r0, newcon(&m->offset, fn), R);
m->offset.type = CUndef;
m->base = r0;
}
}