[PATCH, SMS] Fix violation of memory dependence

[Revital Eres <revital dot eres at linaro dot org>]

Hello,

The attached patch fixes violation of memory dependencies. The
problematic scenario happens when -fmodulo-sched-allow-regmoves flag
is set and certain anti-dep edges are not created.

For example, consider the following three instructions and the edges
between them.  When -fmodulo-sched-allow-regmoves is set the edge (63 -
Anti, 0 -> 64) is not created. (probably due to transitivity)

Insn 63)  r168 = MEM[176]
Out edges: (63 - Anti, 0 -> 64)
In edges: (64 - True, 1 -> 63), (68 - True, 1 -> 63)

insn 64)  176 = 176 + 4
Out edges: (64 - True, 1 -> 63), (64 - True, 0-> 68)
In edges: (63 - Anti, 0 -> 64)

insn 68)  MEM[176 – 4] =  193
Out edges: (68 - True, 1 -> 63)
In edges: (64 - True, 0-> 68)

This anti-dep edge is on the path from one memory instruction to another
--- from 63 to 68; such that removing the edge caused a violation of
the memory dependencies as insn 63 was scheduled after insn 68.

This patch adds intra edges between every two memory instructions in
this case.  It fixes recent bootstrap failure on ARM. (with SMS flags)

The patch was tested as follows:
On ppc64-redhat-linux regtest as well as bootstrap with SMS flags
enabling SMS also on loops with stage count 1.  Regtested on SPU.
On arm-linux-gnueabi bootstrap c language with SMS
flags enabling SMS also on loops with stage count 1
and currently regression testing on c,c++.

OK for mainline once regtest on arm-linux-gnueabi completes?

Thanks,
Revital

Changelog:

gcc/
        * ddg.c (add_intra_loop_mem_dep): New function.
        (build_intra_loop_deps): Call it.

testsuite/
        * gcc.dg/sms-9.c: New file.

Attachment: patch_fix_regmoves_12_6.txt
Description: Text document