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tcg/optimize: Fix sign_mask for logical right-shift

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The 'sign' computation is attempting to locate the sign bit that has
been repeated, so that we can test if that bit is known zero.  That
computation can be zero if there are no known sign repetitions.

Cc: qemu-stable@nongnu.org
Fixes: 93a967fbb5 ("tcg/optimize: Propagate sign info for shifting")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2248
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
(cherry picked from commit 2911e9b95f)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
This commit is contained in:
Richard Henderson
2024-03-26 11:21:38 -10:00
committed by Michael Tokarev
parent d3e9e0fb29
commit 3cdfd68e4e
3 changed files with 30 additions and 1 deletions
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2
tcg/optimize.c
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@ -2123,7 +2123,7 @@ static bool fold_shift(OptContext *ctx, TCGOp *op)
* will not reduced the number of input sign repetitions.
*/
sign = (s_mask & -s_mask) >> 1;
if (!(z_mask & sign)) {
if (sign && !(z_mask & sign)) {
ctx->s_mask = s_mask;
}
break;