Hi,
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77824 reports unreachable code
where MODIFY_EXPR
is being tested instead of SSA_NAME to identify RHS's for copies. This patch
corrects that.
I instrumented the compiler to identify copies being added to the candidate
table, and found
that this now occurs frequently in GCC's support libraries as well as
throughout SPEC CPU2006.
I spot-checked the SLSR dumps for a number of code examples and found that,
while copies often
now appear in the candidate table, and sometimes appear in candidate chains
representing
potential opportunities, I have not yet found a place where this changes code
generation.
Bootstrapped and tested for powerpc64le-unknown-linux-gnu with no regressions,
committed.
Thanks,
Bill
2016-10-10 Bill Schmidt <wschm...@linux.vnet.ibm.com>
PR tree-optimization/77824
* gimple-ssa-strength-reduction.c (stmt_cost): Explicitly return
zero cost for copies.
(find_candidates_dom_walker::before_dom_children): Replace
MODIFY_EXPR with SSA_NAME.
(replace_mult_candidate): Likewise.
(replace_profitable_candidates): Likewise.
Index: gcc/gimple-ssa-strength-reduction.c
===================================================================
--- gcc/gimple-ssa-strength-reduction.c (revision 240924)
+++ gcc/gimple-ssa-strength-reduction.c (working copy)
@@ -688,6 +688,9 @@ stmt_cost (gimple *gs, bool speed)
/* Note that we don't assign costs to copies that in most cases
will go away. */
+ case SSA_NAME:
+ return 0;
+
default:
;
}
@@ -1693,7 +1696,7 @@ find_candidates_dom_walker::before_dom_children (b
gcc_fallthrough ();
CASE_CONVERT:
- case MODIFY_EXPR:
+ case SSA_NAME:
case NEGATE_EXPR:
rhs1 = gimple_assign_rhs1 (gs);
if (TREE_CODE (rhs1) != SSA_NAME)
@@ -1724,7 +1727,7 @@ find_candidates_dom_walker::before_dom_children (b
slsr_process_cast (gs, rhs1, speed);
break;
- case MODIFY_EXPR:
+ case SSA_NAME:
slsr_process_copy (gs, rhs1, speed);
break;
@@ -2010,7 +2013,7 @@ replace_mult_candidate (slsr_cand_t c, tree basis_
&& bump.to_shwi () != HOST_WIDE_INT_MIN
/* It is not useful to replace casts, copies, or adds of
an SSA name and a constant. */
- && cand_code != MODIFY_EXPR
+ && cand_code != SSA_NAME
&& !CONVERT_EXPR_CODE_P (cand_code)
&& cand_code != PLUS_EXPR
&& cand_code != POINTER_PLUS_EXPR
@@ -3445,7 +3448,7 @@ replace_profitable_candidates (slsr_cand_t c)
to a cast or copy. */
if (i >= 0
&& profitable_increment_p (i)
- && orig_code != MODIFY_EXPR
+ && orig_code != SSA_NAME
&& !CONVERT_EXPR_CODE_P (orig_code))
{
if (phi_dependent_cand_p (c))
