![Problem description
r0[r477] = sp + 112;
r0[r565] = sp;
r13 = mem [r0[r565] + 136]
…
r0[r61] = r0[r477] + r5;
The error cause by assign different pseudo register
to same hardware register with live time overlapped.](https://image.slidesharecdn.com/fixgcclrabug-130609093017-phpapp01/85/Fix-gcc-lra-bug-2-320.jpg)
![How to fix the bug
Add offset in register content structure
The offset from eliminate register(sp) to pseudo
register
Update the register content offset when the
eliminate offset have been changed.
r477 = sp’
= sp + 112
sp
SFP
Previous
Eliminate
offset
Current
Eliminate
offsetreg_content_offset[r477]
+=(Curr_elim_offset – prev_elim_offset)](https://image.slidesharecdn.com/fixgcclrabug-130609093017-phpapp01/85/Fix-gcc-lra-bug-5-320.jpg)
Fix gcc lra bug
- 1. Fix LRA assign same hard register with overlapped pseudos Shiva shiva0217@gmail.com May 2013
- 2. Problem description r0[r477] = sp + 112; r0[r565] = sp; r13 = mem [r0[r565] + 136] … r0[r61] = r0[r477] + r5; The error cause by assign different pseudo register to same hardware register with live time overlapped.
- 3. When the r477 have been created r477 = sp’ After the stack have been changed $r477 = sp + 112; r477 = sp’ = sp + 112 sp sp’: old sp sp: new sp
- 4. Why assign to same register? However, when assign hardware register The register content record didn’t notice the pseudo content have been changed It record as (r477 == r565) Therefore, it think live range overlap is OK because the register content is still equal
- 5. How to fix the bug Add offset in register content structure The offset from eliminate register(sp) to pseudo register Update the register content offset when the eliminate offset have been changed. r477 = sp’ = sp + 112 sp SFP Previous Eliminate offset Current Eliminate offsetreg_content_offset[r477] +=(Curr_elim_offset – prev_elim_offset)
- 6. saved arguments for vararg functions Callee saved regs Local variables Outgoing argument Return address Last_frame address (SOFT) FRAME_POINTER ARGUMENT_POINTER HARD_FRAME_POINTER STACK_POINTER
- 7. Relative mailing list http://gcc.gnu.org/ml/gcc/2013-04/msg00144.ht http://gcc.gnu.org/ml/gcc-patches/2013- 04/msg01350.html