https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114490
--- Comment #7 from Kang-Che Sung ---
I just come here to say that PR 114512 is the real issue that I wish to see
fixed. It might be okay for me when the FLAGS of "shl" becomes unused by GCC,
since other than CF (carry) and SF (sign) I don't
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114512
Bug ID: 114512
Summary: Optimization on "test if bit N is set" pattern ((C >>
x) & 1)
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114490
Kang-Che Sung changed:
What|Removed |Added
Resolution|INVALID |---
Status|RESOLVED
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114490
--- Comment #4 from Kang-Che Sung ---
1. I just read "AMD64 Architecture Programmer's Manual - Volume 3:
General-Purpose and System Instructions"
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114496
Bug ID: 114496
Summary: Documentation: "Non-Bugs" page should update/mention
something about -Wsign-conversion
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114490
--- Comment #3 from Kang-Che Sung ---
(In reply to Andrew Pinski from comment #2)
>
> Basically if you are shifting by 0, then the CF bit never changes from the
> previous and this can't be done.
>
> So the comment in the backend is correct
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114490
Bug ID: 114490
Summary: Optimization: x86 "shl" condition codes never reused
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89163
--- Comment #4 from Kang-Che Sung ---
(In reply to Xi Ruoyao from comment #2)
> *** Bug 114406 has been marked as a duplicate of this bug. ***
I can't say bug 114406 is an exact duplicate of this one. Although my report
mainly addresses right
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114406
Bug ID: 114406
Summary: Optimizations with ">>", div, mod and mul where
operands are all positive
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114341
--- Comment #3 from Kang-Che Sung ---
I missed one case that is more obvious:
(1 << __builtin_ctz(y)) == (y & -y)
Multiplication is not needed in this case, and thus (1 << __builtin_ctz(y)) can
simplify to (y & -y). (I didn't think of a reason
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114338
--- Comment #6 from Kang-Che Sung ---
(In reply to Richard Biener from comment #5)
> For canonicalization the BIT_AND variants might be preferable since they
> possibly combine with other logical ops. Also more constant operands
> when the
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114341
Bug ID: 114341
Summary: Optimization opportunity with {mul,div} "(x & -x)" and
{<<,>>} "ctz(x)"
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114338
--- Comment #3 from Kang-Che Sung ---
(In reply to Jakub Jelinek from comment #2)
> Bet the point of this PR is to canonicalize in GIMPLE to one of the forms
> (both have the same number of GIMPLE statements, so that makes it harder to
> pick
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114338
Bug ID: 114338
Summary: (x & (-1 << y)) should be optimized to ((x >> y) << y)
or vice versa
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114087
Bug ID: 114087
Summary: RISC-V optimization on checking certain bits set ((x &
mask) == val)
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113680
--- Comment #3 from Kang-Che Sung ---
Oops. I made a typo in the test code. func4() shouldn't have that redundant
brace.
The corrected example:
```
void func4(int x, int y) {
int diff = x - y;
if (diff > 0)
putchar('>');
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113680
--- Comment #2 from Kang-Che Sung ---
I forgot to mention that such optimization is unsafe for floating points
(actually I knew that when I write my code). `(a - b) < 0` optimization
shouldn't be performed with unsigned integers either. I
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113680
Bug ID: 113680
Summary: Missed optimization: Redundant cmp/test instructions
when comparing (x - y) > 0
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
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