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From: "carrot at google dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/40730] New: redundant memory load Date: Mon, 13 Jul 2009 08:57:00 -0000 [thread overview] Message-ID: <bug-40730-17659@http.gcc.gnu.org/bugzilla/> (raw) Compile the attached source code with options -Os -mthumb -march=armv5te -fno-strict-aliasing, Gcc generates: iterate: push {lr} ldr r3, [r1] // C b .L5 .L4: ldr r3, [r3, #8] // D .L5: str r3, [r0] // A ldr r3, [r0] // B cmp r3, #0 beq .L3 ldr r2, [r3, #4] cmp r2, #0 beq .L4 .L3: str r3, [r0, #12] @ sp needed for prologue pop {pc} Pay attention to instructions marked as A and B. Instruction A store r3 to [r0] but insn B load it back to r3. The instruction A was originally put after instruction C and D. After register allocation, they were allocated to the same registers and looks exactly same. In pass csa, cleanup_cfg was called and it found the same instructions and moved them before instruction B. Now instruction B is obviously redundant. Is it OK to remove this kind of redundant code in pass dce? -- Summary: redundant memory load Product: gcc Version: 4.5.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target 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=40730
next reply other threads:[~2009-07-13 8:57 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2009-07-13 8:57 carrot at google dot com [this message] 2009-07-13 8:58 ` [Bug target/40730] " carrot at google dot com 2009-07-13 9:51 ` rguenth at gcc dot gnu dot org 2009-07-13 10:10 ` steven at gcc dot gnu dot org 2009-07-14 9:14 ` carrot at google dot com 2009-07-14 9:18 ` steven at gcc dot gnu dot org 2009-07-14 9:20 ` steven at gcc dot gnu dot org 2009-07-15 8:07 ` carrot at google dot com 2009-07-15 9:47 ` steven at gcc dot gnu dot org 2010-01-08 9:34 ` steven at gcc dot gnu dot org 2010-01-11 6:47 ` carrot at google dot com 2010-01-11 8:23 ` stevenb dot gcc at gmail dot com 2010-01-11 8:56 ` carrot at google dot com
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