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Fix PR77824

Message ID e43ff334-b79c-c7b7-1cd8-060ff154381a@linux.vnet.ibm.com
State New
Headers show

Commit Message

Bill Schmidt Oct. 10, 2016, 6:54 p.m. UTC 
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  <wschmidt@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.
diff mbox

Patch

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))