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From: "652023330028 at smail dot nju.edu.cn" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/111724] New: [Regression] Missed optimizations probably because of too early arithmetic optimization Date: Sun, 08 Oct 2023 07:55:46 +0000 [thread overview] Message-ID: <bug-111724-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111724 Bug ID: 111724 Summary: [Regression] Missed optimizations probably because of too early arithmetic optimization Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: 652023330028 at smail dot nju.edu.cn Target Milestone: --- Hello, we found some optimizations (probably because of too early arithmetic optimization) that GCC may have missed. We would greatly appreicate if you can take a look and let us know what you think. Given the following code: https://godbolt.org/z/8EW8fx78K int n; void func(int w, int a, int b){ for(int i=0;i<w;i++){ n += (a+a)+(b+b); b += b; } } `a+a` is a loop invariant. But gcc-trunk -O3: func(int, int, int): push {r4, lr} subs lr, r0, #0 ble .L1 movw r4, #:lower16:.LANCHOR0 movt r4, #:upper16:.LANCHOR0 mov ip, #0 ldr r0, [r4] .L3: adds r3, r1, r2 add ip, ip, #1 lsls r2, r2, #1 cmp lr, ip add r0, r0, r3, lsl #1 bne .L3 str r0, [r4] From original(tree): (void) (n = (a + b) * 2 + n) >>>>>; This leads to: _1 = a_11(D) + b_18; _2 = _1 * 2; _4 = _2 + n_lsm.4_7; So, it looks like the missed LICM is due to too early arithmetic optimization. On gcc-6.4, it works as expected. We found that this also affects other optimizations, such as common subexpression elimination. We can provide examples if required. Thank you very much for your time and effort! We look forward to hearing from you.
next reply other threads:[~2023-10-08 7:55 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-10-08 7:55 652023330028 at smail dot nju.edu.cn [this message] 2023-10-09 9:53 ` [Bug tree-optimization/111724] " rguenth at gcc dot gnu.org 2023-10-09 10:34 ` 652023330028 at smail dot nju.edu.cn
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