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Date: Mon, 23 Aug 2004 11:17:00 -0000
From: "falk at debian dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20040823111659.17147.falk@debian.org>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug tree-optimization/17147] New: Alignment information lost with variable size structures
X-Bugzilla-Reason: CC
X-SW-Source: 2004-08/txt/msg02287.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

Given this code:

int f(int n, void *p) {
    struct {
        int a[n];
        int b[n];
    } *sp = p;    
    return sp->b[5];
}

3.4 and 3.5 20040815 (ugh. I should probably try a newer one) generate:

        s4addq $16,$17,$17
        ldl $0,20($17)

while lno generates:
        s4addq $16,$17,$17
        lda $2,20($17)
        ldq_u $3,20($17)
        ldq_u $1,3($2)
        extll $3,$2,$3
        extlh $1,$2,$1
        bis $3,$1,$0
        addl $31,$0,$0

that is, it does an unaligned load. This does not happen at -O0.

-- 
           Summary: Alignment information lost with variable size structures
           Product: gcc
           Version: lno
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: falk at debian dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: alphaev68-unknown-linux-gnu
  GCC host triplet: alphaev68-unknown-linux-gnu
GCC target triplet: alphaev68-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17147