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Revert "tcg/i386: Rely on undefined/undocumented behaviour of BSF/BSR"

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This reverts commit 4ac7691073.

This fixes
  http://lists.nongnu.org/archive/html/qemu-devel/2017-01/msg03062.html

While I think we could get away with relying on the undocumented
behaviour, the tcg constraint system isn't powerful enough to
properly describe the required (non-)overlap conditions.

Reported-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Richard Henderson 2017-01-17 11:38:22 -08:00
parent 23eb9e6b6d
commit 9bf38308f6
1 changed files with 13 additions and 22 deletions
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35
tcg/i386/tcg-target.inc.c
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@ -1148,12 +1148,9 @@ static void tcg_out_ctz(TCGContext *s, int rexw, TCGReg dest, TCGReg arg1,
tcg_debug_assert(arg2 == (rexw ? 64 : 32));
tcg_out_modrm(s, OPC_TZCNT + rexw, dest, arg1);
} else {
/* ??? The manual says that the output is undefined when the
input is zero, but real hardware leaves it unchanged. As
noted in target-i386/translate.c, real programs depend on
this -- now we are one more of those. */
tcg_debug_assert(dest == arg2);
tcg_debug_assert(dest != arg2);
tcg_out_modrm(s, OPC_BSF + rexw, dest, arg1);
tcg_out_cmov(s, TCG_COND_EQ, rexw, dest, arg2);
}
}
@ -1166,26 +1163,20 @@ static void tcg_out_clz(TCGContext *s, int rexw, TCGReg dest, TCGReg arg1,
tcg_debug_assert(arg2 == (rexw ? 64 : 32));
} else {
tcg_debug_assert(dest != arg2);
/* LZCNT sets C if the input was zero. */
tcg_out_cmov(s, TCG_COND_LTU, rexw, dest, arg2);
}
} else {
TCGType type = rexw ? TCG_TYPE_I64: TCG_TYPE_I32;
TCGArg rev = rexw ? 63 : 31;
tcg_debug_assert(!const_a2);
tcg_debug_assert(dest != arg1);
tcg_debug_assert(dest != arg2);
/* Recall that the output of BSR is the index not the count.
Therefore we must adjust the result by ^ (SIZE-1). In some
cases below, we prefer an extra XOR to a JMP. */
/* ??? See the comment in tcg_out_ctz re BSF. */
if (const_a2) {
tcg_debug_assert(dest != arg1);
tcg_out_movi(s, type, dest, arg2 ^ rev);
} else {
tcg_debug_assert(dest == arg2);
tgen_arithi(s, ARITH_XOR + rexw, dest, rev, 0);
}
/* Recall that the output of BSR is the index not the count. */
tcg_out_modrm(s, OPC_BSR + rexw, dest, arg1);
tgen_arithi(s, ARITH_XOR + rexw, dest, rev, 0);
tgen_arithi(s, ARITH_XOR + rexw, dest, rexw ? 63 : 31, 0);
/* Since we have destroyed the flags from BSR, we have to re-test. */
tcg_out_cmp(s, arg1, 0, 1, rexw);
tcg_out_cmov(s, TCG_COND_EQ, rexw, dest, arg2);
}
}
@ -2459,7 +2450,7 @@ static const TCGTargetOpDef *tcg_target_op_def(TCGOpcode op)
case INDEX_op_ctz_i64:
{
static const TCGTargetOpDef ctz[2] = {
{ .args_ct_str = { "r", "r", "0" } },
{ .args_ct_str = { "&r", "r", "r" } },
{ .args_ct_str = { "&r", "r", "rW" } },
};
return &ctz[have_bmi1];
@ -2468,7 +2459,7 @@ static const TCGTargetOpDef *tcg_target_op_def(TCGOpcode op)
case INDEX_op_clz_i64:
{
static const TCGTargetOpDef clz[2] = {
{ .args_ct_str = { "&r", "r", "0i" } },
{ .args_ct_str = { "&r", "r", "r" } },
{ .args_ct_str = { "&r", "r", "rW" } },
};
return &clz[have_lzcnt];