[Bug rtl-optimization/38603] New: IRA does not accommodate LOAD_EXTEND_OP transformations done by combine

[hp at gcc dot gnu dot org]

Trunk revision 141361 with the attached patch shows this regression compared to
unpatched:
Running /home/hp/combx/combined/gcc/testsuite/gcc.c-torture/execute/execute.exp
...
FAIL: gcc.c-torture/execute/20040709-1.c execution,  -O2

However, the regression is hidden at revisions 142609 and 142857.

At the time, a quick glance at the RTL dumps pointed at LOAD_EXTEND_OP
optimizations performed by combine not being properly handled in IRA,
specifically a sign-extension optimized away by combine as matching the
implicit sign extension of a memory read through LOAD_EXTEND_OP.
IIRC the memory read was not being transformed (back) into an explicit
sign-extension.
(I intend to fill in details here, but this will have to do for today.)


-- 
           Summary: IRA does not accommodate LOAD_EXTEND_OP transformations
                    done by combine
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hp at gcc dot gnu dot org
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: mmix-knuth-mmixware


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38603