The following restores copy propagation in CCP for the case the
lattice was constant before trying to transition to a copy. At
some point we changed to use the meet operator to handle
integer constant -> integer constant transitions but that screws
up the const -> copy lattice transition.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
PR tree-optimization/84646
* tree-ssa-ccp.cc (set_lattice_value): Make sure we
allow a const -> copy transition and avoid using meet
in that case.
* gcc.dg/tree-ssa/ssa-ccp-42.c: New testcase.
---
gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-42.c | 26 ++++++++++++++++++++++
gcc/tree-ssa-ccp.cc | 7 +++++-
2 files changed, 32 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-42.c
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-42.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-42.c
new file mode 100644
index 00000000000..b4e5c0f73f2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-ccp-42.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-fgimple -O -fdump-tree-ccp1" } */
+
+__GIMPLE (ssa,startwith("ccp")) int foo (int n)
+{
+ int i;
+ int j;
+
+ __BB(2):
+ i_1 = 0;
+ goto __BB3;
+
+ __BB(3):
+ i_2 = __PHI (__BB2: i_1, __BB3: i_4);
+ j_3 = i_2;
+ i_4 = i_2 + 1;
+ if (i_4 < n_5(D))
+ goto __BB3;
+ else
+ goto __BB4;
+
+ __BB(4):
+ return j_3;
+}
+
+/* { dg-final { scan-tree-dump "return i_2;" "ccp1" } } */
diff --git a/gcc/tree-ssa-ccp.cc b/gcc/tree-ssa-ccp.cc
index 2bcd90646f6..69fd7f1d11d 100644
--- a/gcc/tree-ssa-ccp.cc
+++ b/gcc/tree-ssa-ccp.cc
@@ -532,7 +532,12 @@ set_lattice_value (tree var, ccp_prop_value_t *new_val)
use the meet operator to retain a conservative value.
Missed optimizations like PR65851 makes this necessary.
It also ensures we converge to a stable lattice solution. */
- if (old_val->lattice_val != UNINITIALIZED)
+ if (old_val->lattice_val != UNINITIALIZED
+ /* But avoid using meet for constant -> copy transitions. */
+ && !(old_val->lattice_val == CONSTANT
+ && CONSTANT_CLASS_P (old_val->value)
+ && new_val->lattice_val == CONSTANT
+ && TREE_CODE (new_val->value) == SSA_NAME))
ccp_lattice_meet (new_val, old_val);
gcc_checking_assert (valid_lattice_transition (*old_val, *new_val));
--
2.35.3
