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From: "goon.pri.low at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/112645] New: missed-optimization: cswitch optimization missed in nested if-statement Date: Tue, 21 Nov 2023 01:21:18 +0000 [thread overview] Message-ID: <bug-112645-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112645 Bug ID: 112645 Summary: missed-optimization: cswitch optimization missed in nested if-statement Product: gcc Version: 13.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: goon.pri.low at gmail dot com Target Milestone: --- These two functions should theoretically generate the same code, though the second one uses a constant array. int a(int v) { switch (v & 2) { case 0: //0x switch(v & 1) { case 0: //00 return 643; case 1: //01 return 223; } case 2: //1x switch (v & 1) { case 0: //10 return 444; case 1: //11 return 532; } } } a: test dil, 2 je .L7 and edi, 1 cmp edi, 1 sbb eax, eax and eax, -88 add eax, 532 ret .L7: and edi, 1 cmp edi, 1 sbb eax, eax and eax, 420 add eax, 223 ret int b(int v) { switch (v & 3) { case 0: //00 return 643; case 1: //01 return 223; case 2: //10 return 444; case 3: //11 return 532; } } b: and edi, 3 mov eax, 643 sub edi, 1 cmp edi, 2 ja .L8 mov eax, DWORD PTR CSWTCH.2[0+rdi*4] .L8: ret CSWTCH.2: .long 223 .long 444 .long 532 Additionally while testing this, I found this function which should just use a simple binary and int c(int v) { switch (v & 3) { case 0: return 0; case 1: return 1; case 2: return 2; case 3: return 3; } } c: mov eax, edi and eax, 3 lea edx, [rax-1] cmp edx, 3 mov edx, 0 cmovnb eax, edx ret though has an unnecessary comparison and conditional move?
next reply other threads:[~2023-11-21 1:21 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-11-21 1:21 goon.pri.low at gmail dot com [this message] 2023-11-21 8:23 ` [Bug tree-optimization/112645] " rguenth at gcc dot gnu.org 2023-11-23 21:32 ` goon.pri.low at gmail dot com
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