Hi!
Before the PR58956 fix find_replaceable_in_bb only gave up TER if
stmt was gimple_assign_single_p that was storing something that
could alias with TERed load, but now it also punts on calls (a lot of them
apparently) and inline asm (all of them, because stmt_may_clobber_ref_p
always returns true for GIMPLE_ASM). I believe we can restore TERing
most of the cases for calls and inline asm though, because for calls
all arguments are necessarily evaluated before the call and the only
memory side effects of the call are the call itself and perhaps storing
of non-SSA_NAME return value afterwards. And for inline asm again
all input operands have to be evaluated before the inline asm, and the
only storing side-effects are again inside of the inline asm and perhaps
storing of the output operands.
Thus, this patch will only stop TERing if USE is used somewhere in
lhs of a call for calls or somewhere in output arguments of inline asm.
Bootstrapped/regtested on x86_64-linux and i686-linux (both on trunk and 4.8
branch), ok for trunk/4.8?
The reason I'd like to see this for 4.8 is to decrease the amount of code
generation changes from pre-r205709 to minimum, as it can uncover other
latent bugs than just PR59470.
2013-12-12 Jakub Jelinek <ja...@redhat.com>
PR middle-end/58956
PR middle-end/59470
* tree-ssa-ter.c (find_ssa_name): New helper function.
(find_replaceable_in_bb): For calls, only set same_root_var
if USE is used somewhere in gimple_call_lhs, for GIMPLE_ASM,
only set same_root_var if USE is used somewhere in output operand
trees.
* gcc.target/i386/pr59470.c: New test.
--- gcc/tree-ssa-ter.c.jj 2013-12-10 08:52:13.000000000 +0100
+++ gcc/tree-ssa-ter.c 2013-12-12 10:43:26.177866960 +0100
@@ -554,6 +554,20 @@ mark_replaceable (temp_expr_table_p tab,
}
+/* Helper function for find_replaceable_in_bb. Called via walk_tree to
+ find a SSA_NAME DATA somewhere in *TP. */
+
+static tree
+find_ssa_name (tree *tp, int *walk_subtrees, void *data)
+{
+ tree var = (tree) data;
+ if (*tp == var)
+ return var;
+ else if (IS_TYPE_OR_DECL_P (*tp))
+ *walk_subtrees = 0;
+ return NULL_TREE;
+}
+
/* This function processes basic block BB, and looks for variables which can
be replaced by their expressions. Results are stored in the table TAB. */
@@ -618,7 +632,42 @@ find_replaceable_in_bb (temp_expr_table_
&& gimple_assign_single_p (def_stmt)
&& stmt_may_clobber_ref_p (stmt,
gimple_assign_rhs1 (def_stmt)))
- same_root_var = true;
+ {
+ if (is_gimple_call (stmt))
+ {
+ /* For calls, it is not a problem if USE is among
+ call's arguments or say OBJ_TYPE_REF argument,
+ all those necessarily need to be evaluated before
+ the call that may clobber the memory. But if
+ LHS of the call refers to USE, expansion might
+ evaluate it after the call, prevent TER in that
+ case. */
+ if (gimple_call_lhs (stmt)
+ && TREE_CODE (gimple_call_lhs (stmt)) != SSA_NAME
+ && walk_tree (gimple_call_lhs_ptr (stmt),
+ find_ssa_name, use, NULL))
+ same_root_var = true;
+ }
+ else if (gimple_code (stmt) == GIMPLE_ASM)
+ {
+ /* For inline asm, allow TER of loads into input
+ arguments, but disallow TER for USEs that occur
+ somewhere in outputs. */
+ unsigned int i;
+ for (i = 0; i < gimple_asm_noutputs (stmt); i++)
+ if (TREE_CODE (gimple_asm_output_op (stmt, i))
+ != SSA_NAME
+ && walk_tree (gimple_asm_output_op_ptr (stmt,
+ i),
+ find_ssa_name, use, NULL))
+ {
+ same_root_var = true;
+ break;
+ }
+ }
+ else
+ same_root_var = true;
+ }
}
/* Mark expression as replaceable unless stmt is volatile, or the
--- gcc/testsuite/gcc.target/i386/pr59470.c.jj 2013-12-12 10:31:54.746517544
+0100
+++ gcc/testsuite/gcc.target/i386/pr59470.c 2013-12-12 10:32:42.045273313
+0100
@@ -0,0 +1,17 @@
+/* PR middle-end/58956 */
+/* PR middle-end/59470 */
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+int a, b, d[1024];
+
+int
+main ()
+{
+ int c = a;
+ asm ("{movl $6, (%2); movl $1, %0|mov dword ptr [%2], 6; mov %0, 1}"
+ : "=r" (d[c]) : "rm" (b), "r" (&a) : "memory");
+ if (d[0] != 1 || d[6] != 0)
+ __builtin_abort ();
+ return 0;
+}
Jakub
