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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/109849] New: suboptimal code for vector walking loop Date: Sat, 13 May 2023 22:26:04 +0000 [thread overview] Message-ID: <bug-109849-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109849 Bug ID: 109849 Summary: suboptimal code for vector walking loop Product: gcc Version: 13.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: middle-end Assignee: unassigned at gcc dot gnu.org Reporter: hubicka at gcc dot gnu.org Target Milestone: --- jan@localhost:/tmp> cat t.C #include <vector> typedef unsigned int uint32_t; std::vector<std::pair<uint32_t, uint32_t>> stack; void test() { while (!stack.empty()) { std::pair<uint32_t, uint32_t> cur = stack.back(); stack.pop_back(); if (cur.second) break; } } jan@localhost:/tmp> gcc t.C -O3 -S yields to: _Z4testv: .LFB1264: .cfi_startproc movq stack(%rip), %rcx movq stack+8(%rip), %rax jmp .L5 .p2align 4,,10 .p2align 3 .L6: movl -4(%rax), %edx subq $8, %rax movq %rax, stack+8(%rip) testl %edx, %edx jne .L4 .L5: cmpq %rax, %rcx jne .L6 .L4: ret We really should order the basic blocks putting cmpq before L6 saving a jump. Moreover clang does .p2align 4, 0x90 .LBB1_1: # =>This Inner Loop Header: Depth=1 cmpq %rax, %rcx je .LBB1_3 # %bb.2: # in Loop: Header=BB1_1 Depth=1 cmpl $0, -4(%rcx) leaq -8(%rcx), %rcx movq %rcx, stack+8(%rip) je .LBB1_1 .LBB1_3: retq saving an instruction. Why we do not move stack+8 updating out of the loop?
next reply other threads:[~2023-05-13 22:26 UTC|newest] Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-05-13 22:26 hubicka at gcc dot gnu.org [this message] 2023-05-13 22:32 ` [Bug middle-end/109849] " pinskia at gcc dot gnu.org 2023-05-13 22:40 ` pinskia at gcc dot gnu.org 2023-05-14 5:57 ` amonakov at gcc dot gnu.org 2023-05-14 9:58 ` hubicka at ucw dot cz 2023-05-14 10:01 ` hubicka at ucw dot cz 2023-05-15 6:56 ` rguenth at gcc dot gnu.org 2023-05-17 14:53 ` hubicka at gcc dot gnu.org 2023-05-17 20:36 ` rguenth at gcc dot gnu.org 2023-05-18 9:35 ` hubicka at gcc dot gnu.org 2023-05-18 11:54 ` rguenth at gcc dot gnu.org 2023-05-18 13:00 ` hubicka at gcc dot gnu.org 2023-05-23 9:57 ` cvs-commit at gcc dot gnu.org 2023-05-23 10:10 ` rguenth at gcc dot gnu.org 2023-05-24 11:19 ` cvs-commit at gcc dot gnu.org 2023-06-16 14:20 ` hubicka at gcc dot gnu.org 2023-06-18 16:59 ` cvs-commit at gcc dot gnu.org 2023-06-19 16:28 ` cvs-commit at gcc dot gnu.org 2023-06-26 16:30 ` cvs-commit at gcc dot gnu.org 2023-06-28 9:47 ` cvs-commit at gcc dot gnu.org 2023-06-29 20:46 ` cvs-commit at gcc dot gnu.org 2023-06-30 14:28 ` cvs-commit at gcc dot gnu.org 2023-11-19 15:25 ` hubicka at gcc dot gnu.org 2023-11-21 14:17 ` cvs-commit at gcc dot gnu.org 2023-11-21 15:12 ` hubicka at gcc dot gnu.org 2023-11-24 16:35 ` cvs-commit at gcc dot gnu.org 2023-11-24 17:00 ` cvs-commit at gcc dot gnu.org 2023-11-24 17:00 ` jamborm at gcc dot gnu.org 2023-11-27 14:39 ` rguenth at gcc dot gnu.org 2023-11-28 9:33 ` redi at gcc dot gnu.org 2023-11-28 10:32 ` jamborm at gcc dot gnu.org 2023-11-28 12:41 ` redi at gcc dot gnu.org 2023-11-28 13:29 ` redi at gcc dot gnu.org 2023-11-28 15:29 ` redi at gcc dot gnu.org 2023-11-28 22:21 ` redi at gcc dot gnu.org 2023-11-29 12:27 ` hubicka at ucw dot cz 2023-11-29 15:25 ` cvs-commit at gcc dot gnu.org 2024-01-03 17:41 ` jamborm at gcc dot gnu.org 2024-05-30 11:11 ` redi at gcc dot gnu.org 2024-06-03 19:38 ` cvs-commit at gcc dot gnu.org 2024-06-03 19:54 ` cvs-commit at gcc dot gnu.org
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