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From: "carrot at google dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/41396] New: missed space optimization related to basic block reorder Date: Fri, 18 Sep 2009 07:56:00 -0000 [thread overview] Message-ID: <bug-41396-17659@http.gcc.gnu.org/bugzilla/> (raw) Compile the attached source code with options -march=armv5te -mthumb -Os, I got push {r4, lr} ldr r4, [r0, #8] ldr r3, [r0, #4] b .L2 .L7: ldr r2, [r3, #8] ldr r1, [r2] ldr r2, [r3] add r2, r1, r2 ldr r1, [r3, #4] ldr r1, [r1] sub r2, r2, r1 ldr r1, [r3, #12] cmp r1, #1 beq .L4 cmp r1, #2 bne .L3 b .L12 // C .L4: // ---------BEGIN BLOCK B ldr r1, [r0] neg r1, r1 cmp r2, r1 bge .L3 b .L9 // ----------END BLOCK B .L12: // ---------------BEGIN BLOCK A------- ldr r1, [r0] cmp r2, r1 bgt .L9 .L3: add r3, r3, #16 .L2: cmp r3, r4 bcc .L7 mov r0, #0 b .L6 // -----------------END BLOCK A--------- .L9: mov r0, #1 .L6: @ sp needed for prologue pop {r4, pc} If we change the order of block A and block B, we can remove 2 branch instructions, inst C and another inst at the end of block B. Need new basic block reorder algorithm for code size optimization? -- Summary: missed space optimization related to basic block reorder Product: gcc Version: 4.5.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: middle-end AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: carrot at google dot com GCC build triplet: i686-linux GCC host triplet: i686-linux GCC target triplet: arm-eabi http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41396
next reply other threads:[~2009-09-18 7:56 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2009-09-18 7:56 carrot at google dot com [this message] 2009-09-18 7:57 ` [Bug middle-end/41396] " pinskia at gcc dot gnu dot org 2009-09-18 7:57 ` carrot at google dot com 2009-09-18 8:44 ` rguenth at gcc dot gnu dot org 2009-09-20 21:07 ` pinskia at gcc dot gnu dot org
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