[PATCH] tree-optimization/103596 - fix missed propagation into switches
Richard Biener
rguenther@suse.de
Tue Dec 7 13:07:26 GMT 2021
may_propagate_copy unnecessarily restricts propagating non-abnormals
into places that currently contain an abnormal SSA name but are
not the PHI argument for an abnormal edge. This causes VN to
not elide a CFG path that it assumes is elided, resulting in
released SSA names in the IL.
The fix is to enhance the may_propagate_copy API to specify the
destination is _not_ a PHI argument. I chose to not update only
the relevant caller in VN and the may_propagate_copy_into_stmt API
at this point because this is a regression and needs backporting.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
2021-12-07 Richard Biener <rguenther@suse.de>
PR tree-optimization/103596
* tree-ssa-sccvn.c (eliminate_dom_walker::eliminate_stmt):
Note we are not propagating into a PHI argument to may_propagate_copy.
* tree-ssa-propagate.h (may_propagate_copy): Add
argument specifying whether we propagate into a PHI arg.
* tree-ssa-propagate.c (may_propagate_copy): Likewise.
When not doing so we can replace an abnormal with
something else.
(may_propagate_into_stmt): Update may_propagate_copy calls.
(replace_exp_1): Move propagation checking code to
propagate_value and rename to ...
(replace_exp): ... this and elide previous wrapper.
(propagate_value): Perform checking with adjusted
may_propagate_copy call and dispatch to replace_exp.
* gcc.dg/torture/pr103596.c: New testcase.
---
gcc/testsuite/gcc.dg/torture/pr103596.c | 36 ++++++++++++++
gcc/tree-ssa-propagate.c | 62 ++++++++++---------------
gcc/tree-ssa-propagate.h | 2 +-
gcc/tree-ssa-sccvn.c | 2 +-
4 files changed, 62 insertions(+), 40 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/torture/pr103596.c
diff --git a/gcc/testsuite/gcc.dg/torture/pr103596.c b/gcc/testsuite/gcc.dg/torture/pr103596.c
new file mode 100644
index 00000000000..4f65c36d121
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr103596.c
@@ -0,0 +1,36 @@
+/* { dg-do compile } */
+/* { dg-additional-options "--param case-values-threshold=1" } */
+
+int n;
+
+void
+qux (int a)
+{
+}
+
+int
+baz (void)
+{
+ return -1;
+}
+
+__attribute__ ((returns_twice)) int
+bar (int b)
+{
+ if (n != 0)
+ {
+ if (b != 2)
+ if (b != 0)
+ return n + b;
+
+ if (n == 2)
+ return 0;
+ }
+}
+
+void
+foo (void)
+{
+ qux (n);
+ bar (baz ());
+}
diff --git a/gcc/tree-ssa-propagate.c b/gcc/tree-ssa-propagate.c
index 6d19410caa8..1f2a17f73c9 100644
--- a/gcc/tree-ssa-propagate.c
+++ b/gcc/tree-ssa-propagate.c
@@ -1042,10 +1042,12 @@ substitute_and_fold_engine::substitute_and_fold (basic_block block)
}
-/* Return true if we may propagate ORIG into DEST, false otherwise. */
+/* Return true if we may propagate ORIG into DEST, false otherwise.
+ If DEST_NOT_PHI_ARG_P is true then assume the propagation does
+ not happen into a PHI argument which relaxes some constraints. */
bool
-may_propagate_copy (tree dest, tree orig)
+may_propagate_copy (tree dest, tree orig, bool dest_not_phi_arg_p)
{
tree type_d = TREE_TYPE (dest);
tree type_o = TREE_TYPE (orig);
@@ -1065,8 +1067,10 @@ may_propagate_copy (tree dest, tree orig)
&& SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig))
return false;
/* Similarly if DEST flows in from an abnormal edge then the copy cannot be
- propagated. */
- else if (TREE_CODE (dest) == SSA_NAME
+ propagated. If we know we do not propagate into a PHI argument this
+ does not apply. */
+ else if (!dest_not_phi_arg_p
+ && TREE_CODE (dest) == SSA_NAME
&& SSA_NAME_OCCURS_IN_ABNORMAL_PHI (dest))
return false;
@@ -1100,9 +1104,9 @@ may_propagate_copy_into_stmt (gimple *dest, tree orig)
for the expression, so we delegate to may_propagate_copy. */
if (gimple_assign_single_p (dest))
- return may_propagate_copy (gimple_assign_rhs1 (dest), orig);
+ return may_propagate_copy (gimple_assign_rhs1 (dest), orig, true);
else if (gswitch *dest_swtch = dyn_cast <gswitch *> (dest))
- return may_propagate_copy (gimple_switch_index (dest_swtch), orig);
+ return may_propagate_copy (gimple_switch_index (dest_swtch), orig, true);
/* In other cases, the expression is not materialized, so there
is no destination to pass to may_propagate_copy. On the other
@@ -1140,25 +1144,19 @@ may_propagate_copy_into_asm (tree dest ATTRIBUTE_UNUSED)
}
-/* Common code for propagate_value and replace_exp.
+/* Replace *OP_P with value VAL (assumed to be a constant or another SSA_NAME).
- Replace use operand OP_P with VAL. FOR_PROPAGATION indicates if the
- replacement is done to propagate a value or not. */
+ Use this version when not const/copy propagating values. For example,
+ PRE uses this version when building expressions as they would appear
+ in specific blocks taking into account actions of PHI nodes.
-static void
-replace_exp_1 (use_operand_p op_p, tree val,
- bool for_propagation ATTRIBUTE_UNUSED)
-{
- if (flag_checking)
- {
- tree op = USE_FROM_PTR (op_p);
- gcc_assert (!(for_propagation
- && TREE_CODE (op) == SSA_NAME
- && TREE_CODE (val) == SSA_NAME
- && !may_propagate_copy (op, val)));
- }
+ The statement in which an expression has been replaced should be
+ folded using fold_stmt_inplace. */
- if (TREE_CODE (val) == SSA_NAME)
+void
+replace_exp (use_operand_p op_p, tree val)
+{
+ if (TREE_CODE (val) == SSA_NAME || CONSTANT_CLASS_P (val))
SET_USE (op_p, val);
else
SET_USE (op_p, unshare_expr (val));
@@ -1174,22 +1172,10 @@ replace_exp_1 (use_operand_p op_p, tree val,
void
propagate_value (use_operand_p op_p, tree val)
{
- replace_exp_1 (op_p, val, true);
-}
-
-/* Replace *OP_P with value VAL (assumed to be a constant or another SSA_NAME).
-
- Use this version when not const/copy propagating values. For example,
- PRE uses this version when building expressions as they would appear
- in specific blocks taking into account actions of PHI nodes.
-
- The statement in which an expression has been replaced should be
- folded using fold_stmt_inplace. */
-
-void
-replace_exp (use_operand_p op_p, tree val)
-{
- replace_exp_1 (op_p, val, false);
+ if (flag_checking)
+ gcc_assert (may_propagate_copy (USE_FROM_PTR (op_p), val,
+ !is_a <gphi *> (USE_STMT (op_p))));
+ replace_exp (op_p, val);
}
diff --git a/gcc/tree-ssa-propagate.h b/gcc/tree-ssa-propagate.h
index 5257fbb0cf8..87a94ad17c3 100644
--- a/gcc/tree-ssa-propagate.h
+++ b/gcc/tree-ssa-propagate.h
@@ -65,7 +65,7 @@ enum ssa_prop_result {
extern void move_ssa_defining_stmt_for_defs (gimple *, gimple *);
extern bool stmt_makes_single_store (gimple *);
-extern bool may_propagate_copy (tree, tree);
+extern bool may_propagate_copy (tree, tree, bool = false);
extern bool may_propagate_copy_into_stmt (gimple *, tree);
extern bool may_propagate_copy_into_asm (tree);
extern void propagate_value (use_operand_p, tree);
diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index d31bf329d2e..16c93d1be78 100644
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -6607,7 +6607,7 @@ eliminate_dom_walker::eliminate_stmt (basic_block b, gimple_stmt_iterator *gsi)
at the definition are also available at uses. */
sprime = eliminate_avail (gimple_bb (SSA_NAME_DEF_STMT (use)), use);
if (sprime && sprime != use
- && may_propagate_copy (use, sprime)
+ && may_propagate_copy (use, sprime, true)
/* We substitute into debug stmts to avoid excessive
debug temporaries created by removed stmts, but we need
to avoid doing so for inserted sprimes as we never want
--
2.31.1
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