[PATCH] Fix SLSR conditional candidate bug with commuted operands

[Bill Schmidt]

This fixes the following bug:

On Mon, 2013-05-06 at 21:25 +0200, Jakub Jelinek wrote:
> On Sun, May 05, 2013 at 03:45:17PM -0500, Bill Schmidt wrote:
> > 2013-05-05  Bill Schmidt  <wschm...@linux.vnet.ibm.com>
> > 
> >     * gimple-ssa-strength-reduction.c (slsr_process_phi): Re-enable.
> >     (find_candidates_in_block): Re-enable slsr_process_phi.
> >     (create_phi_basis): Fix double counting of candidate adjustment.
> 
> This broke gcc.dg/pr33017.c testcase on i?86/x86_64 -m32.
> ./cc1 -O2 -ftree-vectorize -m32 -mno-sse pr33017.c
> difference between r19862{6,7} is:
> --- pr33017.s1        2013-05-06 21:22:03.786745422 +0200
> +++ pr33017.s2        2013-05-06 21:22:16.844673015 +0200
> @@ -32,9 +32,9 @@ foo:
>       movb    $87, var.1373+2(%eax)
>       je      .L10
>       cmpl    $3, %edx
> -     movb    $87, var.1373+3(%eax)
> +     movb    $87, var.1373+2(%eax,%eax)
>       jne     .L11
> -     movb    $87, var.1373+4(%eax)
> +     movb    $87, var.1373+2(%eax,%eax,2)
>       movl    $3, %ebp
>       movl    $61, 28(%esp)
>  .L3:
> 
>       Jakub
> 

The pattern we seek for replacing a conditional candidate can be
confused when a CAND_ADD with an index of 1 has its operands commuted in
the analysis.  (For x = y + z, we may record two CAND_ADDs, one for
either ordering of the addends.)  For a candidate with reversed addends
in the analysis, don't attempt to find a hidden basis.  Otherwise we
make an invalid replacement later on.

Verified this fixes the reported bug.  Bootstrapped and tested on
powerpc64-unknown-linux-gnu with no new regressions.  Ok for trunk?

Thanks,
Bill


2013-05-06  Bill Schmidt  <wschm...@linux.vnet.ibm.com>

        * gimple-ssa-strength-reduction.c (find_phi_def): Don't record a
        phi def as possibly hiding a basis for a CAND_ADD whose operands
        have been commuted in the analysis.
        (alloc_cand_and_find_basis): Add parms to call to find_phi_def.


Index: gcc/gimple-ssa-strength-reduction.c
===================================================================
--- gcc/gimple-ssa-strength-reduction.c (revision 198627)
+++ gcc/gimple-ssa-strength-reduction.c (working copy)
@@ -413,15 +413,29 @@ cand_chain_hasher::equal (const value_type *chain1
 static hash_table <cand_chain_hasher> base_cand_map;
 
 /* Look in the candidate table for a CAND_PHI that defines BASE and
-   return it if found; otherwise return NULL.  */
+   return it if found; otherwise return NULL.  GS is the candidate
+   statement with BASE, INDEX, and STRIDE.  If GS is a CAND_ADD with
+   an index of 1 and an SSA name for STRIDE, we must be careful that
+   we haven't commuted the operands for this candidate.  STRIDE must
+   correspond to the second addend of GS for the eventual transformation
+   to be legal.  If not, return NULL.  */
 
 static cand_idx
-find_phi_def (tree base)
+find_phi_def (gimple gs, enum cand_kind kind, tree base,
+              double_int index, tree stride)
 {
   slsr_cand_t c;
 
   if (TREE_CODE (base) != SSA_NAME)
     return 0;
+
+  /* Check for commutativity condition.  */
+  if (kind == CAND_ADD
+      && index.is_one ()
+      && TREE_CODE (stride) == SSA_NAME
+      && gimple_assign_rhs_code (gs) == PLUS_EXPR
+      && stride != gimple_assign_rhs2 (gs))
+    return 0;
   
   c = base_cand_from_table (base);
 
@@ -565,7 +579,7 @@ alloc_cand_and_find_basis (enum cand_kind kind, gi
   c->next_interp = 0;
   c->dependent = 0;
   c->sibling = 0;
-  c->def_phi = find_phi_def (base);
+  c->def_phi = find_phi_def (gs, kind, base, index, stride);
   c->dead_savings = savings;
 
   cand_vec.safe_push (c);