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6g: avoid unnecessary conversion in shift bounds check

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R=ken2
CC=golang-dev
https://golang.org/cl/1278042
This commit is contained in:
Russ Cox 2010-05-24 15:30:53 -07:00
parent 426fef5585
commit d14baee96e
1 changed files with 15 additions and 4 deletions
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19
src/cmd/6g/ggen.c
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@ -888,6 +888,7 @@ cgen_shift(int op, Node *nl, Node *nr, Node *res)
int a, rcx;
Prog *p1;
uvlong sc;
Type *tcount;
a = optoas(op, nl->type);
@ -920,8 +921,16 @@ cgen_shift(int op, Node *nl, Node *nr, Node *res)
rcx = reg[D_CX];
nodreg(&n1, types[TUINT32], D_CX);
// Allow either uint32 or uint64 as shift type,
// to avoid unnecessary conversion from uint32 to uint64
// just to do the comparison.
tcount = types[simtype[nr->type->etype]];
if(tcount->etype < TUINT32)
tcount = types[TUINT32];
regalloc(&n1, nr->type, &n1); // to hold the shift type in CX
regalloc(&n3, types[TUINT64], &n1); // to clear high bits of CX
regalloc(&n3, tcount, &n1); // to clear high bits of CX
nodreg(&cx, types[TUINT64], D_CX);
memset(&oldcx, 0, sizeof oldcx);
@ -929,6 +938,7 @@ cgen_shift(int op, Node *nl, Node *nr, Node *res)
regalloc(&oldcx, types[TUINT64], N);
gmove(&cx, &oldcx);
}
cx.type = tcount;
if(samereg(&cx, res))
regalloc(&n2, nl->type, N);
@ -946,9 +956,9 @@ cgen_shift(int op, Node *nl, Node *nr, Node *res)
regfree(&n3);
// test and fix up large shifts
nodconst(&n3, types[TUINT64], nl->type->width*8);
gins(optoas(OCMP, types[TUINT64]), &n1, &n3);
p1 = gbranch(optoas(OLT, types[TUINT64]), T);
nodconst(&n3, tcount, nl->type->width*8);
gins(optoas(OCMP, tcount), &n1, &n3);
p1 = gbranch(optoas(OLT, tcount), T);
if(op == ORSH && issigned[nl->type->etype]) {
nodconst(&n3, types[TUINT32], nl->type->width*8-1);
gins(a, &n3, &n2);
@ -960,6 +970,7 @@ cgen_shift(int op, Node *nl, Node *nr, Node *res)
gins(a, &n1, &n2);
if(oldcx.op != 0) {
cx.type = types[TUINT64];
gmove(&oldcx, &cx);
regfree(&oldcx);
}