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