When facing multiple PHI defs and one feeding the other we can
postpone processing uses of one and thus can proceed.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
2022-05-20 Richard Biener <rguent...@suse.de>
PR tree-optimization/100221
* tree-ssa-dse.cc (contains_phi_arg): New function.
(dse_classify_store): Postpone PHI defs that feed another PHI in defs.
* gcc.dg/tree-ssa/ssa-dse-44.c: New testcase.
* gcc.dg/tree-ssa/ssa-dse-45.c: Likewise.
---
gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-44.c | 19 +++++++++
gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-45.c | 24 +++++++++++
gcc/tree-ssa-dse.cc | 46 +++++++++++++++++++---
3 files changed, 84 insertions(+), 5 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-44.c
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-45.c
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-44.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-44.c
new file mode 100644
index 00000000000..aaec41d7bdf
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-44.c
@@ -0,0 +1,19 @@
+/* { dg-do link } */
+/* { dg-options "-O -fdump-tree-dse1-details" } */
+
+extern void foo(void);
+int a, b;
+static int c;
+int main()
+{
+ if (c)
+ foo ();
+ int *g = &c;
+ int **h = &g;
+ int ***h1 = &h;
+ if (a)
+ while (b)
+ b = 0;
+}
+
+/* { dg-final { scan-tree-dump "Deleted dead store: g = &c;" "dse1" } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-45.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-45.c
new file mode 100644
index 00000000000..fd92d7b599a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-45.c
@@ -0,0 +1,24 @@
+/* { dg-do link } */
+/* { dg-options "-O" } */
+
+extern void foo(void);
+int a, b;
+static int c;
+static void f() {
+ while (a)
+ for (; b; b--)
+ ;
+}
+void i() {
+ if (c)
+ foo();
+ int *g = &c;
+ {
+ int **h[1] = {&g};
+ f();
+ }
+}
+int main() {
+ i();
+ return 0;
+}
diff --git a/gcc/tree-ssa-dse.cc b/gcc/tree-ssa-dse.cc
index 881a2d0f98d..ea50de789b1 100644
--- a/gcc/tree-ssa-dse.cc
+++ b/gcc/tree-ssa-dse.cc
@@ -898,6 +898,17 @@ dse_optimize_redundant_stores (gimple *stmt)
}
}
+/* Return whether PHI contains ARG as an argument. */
+
+static bool
+contains_phi_arg (gphi *phi, tree arg)
+{
+ for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i)
+ if (gimple_phi_arg_def (phi, i) == arg)
+ return true;
+ return false;
+}
+
/* A helper of dse_optimize_stmt.
Given a GIMPLE_ASSIGN in STMT that writes to REF, classify it
according to downstream uses and defs. Sets *BY_CLOBBER_P to true
@@ -949,8 +960,8 @@ dse_classify_store (ao_ref *ref, gimple *stmt,
return DSE_STORE_LIVE;
auto_vec<gimple *, 10> defs;
- gimple *first_phi_def = NULL;
- gimple *last_phi_def = NULL;
+ gphi *first_phi_def = NULL;
+ gphi *last_phi_def = NULL;
FOR_EACH_IMM_USE_STMT (use_stmt, ui, defvar)
{
/* Limit stmt walking. */
@@ -973,8 +984,8 @@ dse_classify_store (ao_ref *ref, gimple *stmt,
{
defs.safe_push (use_stmt);
if (!first_phi_def)
- first_phi_def = use_stmt;
- last_phi_def = use_stmt;
+ first_phi_def = as_a <gphi *> (use_stmt);
+ last_phi_def = as_a <gphi *> (use_stmt);
}
}
/* If the statement is a use the store is not dead. */
@@ -1046,6 +1057,7 @@ dse_classify_store (ao_ref *ref, gimple *stmt,
use_operand_p use_p;
tree vdef = (gimple_code (def) == GIMPLE_PHI
? gimple_phi_result (def) : gimple_vdef (def));
+ gphi *phi_def;
/* If the path to check starts with a kill we do not need to
process it further.
??? With byte tracking we need only kill the bytes currently
@@ -1079,7 +1091,31 @@ dse_classify_store (ao_ref *ref, gimple *stmt,
&& bitmap_bit_p (visited,
SSA_NAME_VERSION
(PHI_RESULT (use_stmt))))))
- defs.unordered_remove (i);
+ {
+ defs.unordered_remove (i);
+ if (def == first_phi_def)
+ first_phi_def = NULL;
+ else if (def == last_phi_def)
+ last_phi_def = NULL;
+ }
+ /* If def is a PHI and one of its arguments is another PHI node still
+ in consideration we can defer processing it. */
+ else if ((phi_def = dyn_cast <gphi *> (def))
+ && ((last_phi_def
+ && phi_def != last_phi_def
+ && contains_phi_arg (phi_def,
+ gimple_phi_result (last_phi_def)))
+ || (first_phi_def
+ && phi_def != first_phi_def
+ && contains_phi_arg
+ (phi_def, gimple_phi_result (first_phi_def)))))
+ {
+ defs.unordered_remove (i);
+ if (phi_def == first_phi_def)
+ first_phi_def = NULL;
+ else if (phi_def == last_phi_def)
+ last_phi_def = NULL;
+ }
else
++i;
}
--
2.35.3
