https://bugs.kde.org/show_bug.cgi?id=417187
Bug ID: 417187
Summary: [MIPS] Conditional branch problem since 'grail'
changes
Product: valgrind
Version: 3.15 SVN
Platform: Other
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: jsew...@acm.org
Reporter: stefan.maksimo...@rt-rk.com
Target Milestone: ---
Created attachment 125689
--> https://bugs.kde.org/attachment.cgi?id=125689&action=edit
enable_grail_mips.diff
The problem we're having is present since the recent changes from the 'grail'
branch have been applied to master.
It can be reproduced on a simple program (consists just of the main function
that has a return 42; statement).
More specifically, it happens even before main is encountered (in the
_dl_aux_init function).
The attached debug output depicts inconsistent IR which causes the failure:
t5 = CmpEQ32(t4,0x0:I32)
...
PUT(136) = t5
The number 136 corresponds with the PC register.
Valgrind tries to write the result of the compare operation into the PC
register.
The following is a different observation which may or may not have to do with
the problem above:
It has to do with conditional branches. Namely, upon hitting such a branch
three instructions are analysed for each of those.
The problem seems to be having a branch instruction as the last one of those
three.
Since branch instructions on MIPS have delay slots, the delay slot instruction
needs to be analysed before the jump kind can be set
to the branch instruction preceding it.
As it stands that doesn't happen and the jump instruction gets assigned a jump
kind of Ijk_Boring instead of Ijk_Call.
See the fall through case after superblock 4 in the attached debug output.
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