| Summary: | missed space optimization related to basic block reorder | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Carrot <carrot> |
| Component: | rtl-optimization | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | NEW --- | ||
| Severity: | enhancement | CC: | carrot, dimhen, gabravier, gcc-bugs, icera-sdkteam-gnu, ktietz, pinskia, rguenth |
| Priority: | P3 | Keywords: | missed-optimization |
| Version: | 4.5.0 | ||
| Target Milestone: | --- | ||
| See Also: | https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40730 | ||
| Host: | i686-linux | Target: | arm-eabi |
| Build: | i686-linux | Known to work: | |
| Known to fail: | Last reconfirmed: | 2009-09-18 08:44:20 | |
| Attachments: | test case | ||
Created attachment 18602 [details]
test case
yes, currently at -Os basic block reordering is disabled :). So, confirmed. BB reordering is enabled at -Os now using the "simple" (non-STV) algorithm, but for the testcase I don't see it's better now. |
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?