[Bug c/35178] New: Misaligned Accesses on arrays of packed stucts

[Bug c/35178] New: Misaligned Accesses on arrays of packed stucts

[chrbr at gcc dot gnu dot org]

This bug was noticed on sh but potentially impacts other STRICT_ALIGNMENT
targets. 

The attached test case reduces a misaligned field access from an array of
packed structs. In this example compiled with -O2 the field wMaxPacketSize is
accessed (on sh4) with a mov.w instruction although it is byte aligned.

It seems that the tree-ssa-loop ivopts did not check packed struct offsets
indexed by an induction variable. Thus if the struct size is not aligned, the
field  becomes unaligned after the first iteration even if it was aligned from
the base of this structure.

The proposed patch solves this problem by expanding may_be_unaligned_p to check
that a loop carried offset is a multiple of the desired alignment.


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           Summary: Misaligned Accesses on arrays of packed stucts
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: chrbr at gcc dot gnu dot org
GCC target triplet: sh4-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35178

[Bug c/35178] Misaligned Accesses on arrays of packed stucts

[chrbr at gcc dot gnu dot org]

------- Comment #1 from chrbr at gcc dot gnu dot org  2008-02-13 13:42 -------
Created an attachment (id=15138)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15138&action=view)
gcc testsuite case


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35178

[Bug c/35178] Misaligned Accesses on arrays of packed stucts

[chrbr at gcc dot gnu dot org]

------- Comment #2 from chrbr at gcc dot gnu dot org  2008-02-13 13:45 -------
Created an attachment (id=15139)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=15139&action=view)
Proposed patch

regression tested on sh-superh-elf and sh4-linux-gnu.
and bootstraped for i686-pc-linux-gnu. 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35178

[Bug c/35178] Misaligned Accesses on arrays of packed stucts

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2008-02-13 14:27 -------
patches should be sent to the gcc-patches mailing list.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35178

[Bug tree-optimization/35178] Misaligned Accesses on arrays of packed stucts

[chrbr at gcc dot gnu dot org]

------- Comment #4 from chrbr at gcc dot gnu dot org  2008-02-19 07:53 -------
fixed in mainline


-- 

chrbr at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |http://gcc.gnu.org/ml/gcc-
                   |                            |patches/2008-
                   |                            |02/msg00690.html
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35178