[PATCH] Fix PR42438
Richard Guenther
rguenther@suse.de
Sun Jan 3 11:59:00 GMT 2010
This fixes some of the fallout of the fix of PR38819 by implementing
it in a more efficient and precise way. PR38819 is about us
PREing trapping expressions where the path from the insertion point
to the redundant expression contains side-effects such as possibly
not returning calls. The original fix simply avoided inserting
trapping expressions at all - which is overly conservative and
for example will never PRE integer divisions which is clearly
bad. The following alternate fix instead tries to compute the
'contains side-effects on the path' property during antic set
cleaning thereby simulating noreturn edges from such calls.
(All non-const or looping calls are possibly not returning,
if we ever compute this property more precise we have to resort
to the side-effects notion again (consider __builtin_puts which
does return but clearly has side-effects)).
Simluating the extra edges in clean doesn't simulate the split
blocks, thus even calls after the original trapping expression
in the same basic-block will prohibit the PRE. Still better
than before.
Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
Richard.
2010-01-03 Richard Guenther <rguenther@suse.de>
PR tree-optimization/42438
* tree-ssa-pre.c (struct bb_bitmap_sets): Add
contains_may_not_return_call flag.
(BB_MAY_NOTRETURN): New.
(valid_in_sets): Trapping nary operations are not valid
in blocks that may not return.
(insert_into_preds_of_block): Remove check for trapping
expressions.
(compute_avail): Compute also BB_MAY_NOTRETURN.
* gcc.dg/tree-ssa/ssa-pre-27.c: New testcase.
Index: gcc/tree-ssa-pre.c
===================================================================
*** gcc/tree-ssa-pre.c (revision 155576)
--- gcc/tree-ssa-pre.c (working copy)
*************** typedef struct bb_bitmap_sets
*** 382,392 ****
bitmap expr_dies;
/* True if we have visited this block during ANTIC calculation. */
! unsigned int visited:1;
/* True we have deferred processing this block during ANTIC
calculation until its successor is processed. */
unsigned int deferred : 1;
} *bb_value_sets_t;
#define EXP_GEN(BB) ((bb_value_sets_t) ((BB)->aux))->exp_gen
--- 382,395 ----
bitmap expr_dies;
/* True if we have visited this block during ANTIC calculation. */
! unsigned int visited : 1;
/* True we have deferred processing this block during ANTIC
calculation until its successor is processed. */
unsigned int deferred : 1;
+
+ /* True when the block contains a call that might not return. */
+ unsigned int contains_may_not_return_call : 1;
} *bb_value_sets_t;
#define EXP_GEN(BB) ((bb_value_sets_t) ((BB)->aux))->exp_gen
*************** typedef struct bb_bitmap_sets
*** 399,404 ****
--- 402,408 ----
#define EXPR_DIES(BB) ((bb_value_sets_t) ((BB)->aux))->expr_dies
#define BB_VISITED(BB) ((bb_value_sets_t) ((BB)->aux))->visited
#define BB_DEFERRED(BB) ((bb_value_sets_t) ((BB)->aux))->deferred
+ #define BB_MAY_NOTRETURN(BB) ((bb_value_sets_t) ((BB)->aux))->contains_may_not_return_call
/* Basic block list in postorder. */
*************** valid_in_sets (bitmap_set_t set1, bitmap
*** 2032,2037 ****
--- 2036,2048 ----
return false;
}
}
+ /* If the NARY may trap make sure the block does not contain
+ a possible exit point.
+ ??? This is overly conservative if we translate AVAIL_OUT
+ as the available expression might be after the exit point. */
+ if (BB_MAY_NOTRETURN (block)
+ && vn_nary_may_trap (nary))
+ return false;
return true;
}
break;
*************** compute_antic (void)
*** 2469,2474 ****
--- 2480,2486 ----
BB_VISITED (block) = 0;
BB_DEFERRED (block) = 0;
+
/* While we are here, give empty ANTIC_IN sets to each block. */
ANTIC_IN (block) = bitmap_set_new ();
PA_IN (block) = bitmap_set_new ();
*************** insert_into_preds_of_block (basic_block
*** 3187,3202 ****
}
}
- /* Make sure we are not inserting trapping expressions. */
- FOR_EACH_EDGE (pred, ei, block->preds)
- {
- bprime = pred->src;
- eprime = avail[bprime->index];
- if (eprime->kind == NARY
- && vn_nary_may_trap (PRE_EXPR_NARY (eprime)))
- return false;
- }
-
/* Make the necessary insertions. */
FOR_EACH_EDGE (pred, ei, block->preds)
{
--- 3199,3204 ----
*************** compute_avail (void)
*** 3804,3809 ****
--- 3806,3813 ----
for (gsi = gsi_start_phis (block); !gsi_end_p (gsi); gsi_next (&gsi))
make_values_for_phi (gsi_stmt (gsi), block);
+ BB_MAY_NOTRETURN (block) = 0;
+
/* Now compute value numbers and populate value sets with all
the expressions computed in BLOCK. */
for (gsi = gsi_start_bb (block); !gsi_end_p (gsi); gsi_next (&gsi))
*************** compute_avail (void)
*** 3814,3819 ****
--- 3818,3840 ----
stmt = gsi_stmt (gsi);
gimple_set_uid (stmt, stmt_uid++);
+ /* Cache whether the basic-block has any non-visible side-effect
+ or control flow.
+ If this isn't a call or it is the last stmt in the
+ basic-block then the CFG represents things correctly. */
+ if (is_gimple_call (stmt)
+ && !stmt_ends_bb_p (stmt))
+ {
+ /* Non-looping const functions always return normally.
+ Otherwise the call might not return or have side-effects
+ that forbids hoisting possibly trapping expressions
+ before it. */
+ int flags = gimple_call_flags (stmt);
+ if (!(flags & ECF_CONST)
+ || (flags & ECF_LOOPING_CONST_OR_PURE))
+ BB_MAY_NOTRETURN (block) = 1;
+ }
+
FOR_EACH_SSA_TREE_OPERAND (op, stmt, iter, SSA_OP_DEF)
{
pre_expr e = get_or_alloc_expr_for_name (op);
Index: gcc/testsuite/gcc.dg/tree-ssa/ssa-pre-27.c
===================================================================
*** gcc/testsuite/gcc.dg/tree-ssa/ssa-pre-27.c (revision 0)
--- gcc/testsuite/gcc.dg/tree-ssa/ssa-pre-27.c (revision 0)
***************
*** 0 ****
--- 1,29 ----
+ /* { dg-do compile } */
+ /* { dg-options "-O2 -fdump-tree-pre" } */
+
+ int foo (int i, int j, int b)
+ {
+ int res = 0;
+ if (b)
+ res = i/j;
+ /* We should insert the possibly trapping i/j. */
+ res += i/j;
+ return res;
+ }
+
+ extern void bar (void);
+ int foo2 (int i, int j, int b)
+ {
+ int res = 0;
+ if (b)
+ res = i/j;
+ /* But we fail so here because of the possibly not returning
+ call in the same basic-block. */
+ res += i/j;
+ bar ();
+ return res;
+ }
+
+ /* { dg-final { scan-tree-dump-times "# prephitmp" 1 "pre" } } */
+ /* { dg-final { scan-tree-dump-times "# prephitmp" 2 "pre" { xfail *-*-* } } } */
+ /* { dg-final { cleanup-tree-dump "pre" } } */
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