https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37242
--- Comment #26 from Richard Biener <rguenth at gcc dot gnu.org> ---
/* Match arithmetic done in a different type where we can easily
substitute the result from some earlier sign-changed or widened
operation. */
if (INTEGRAL_TYPE_P (type)
&& TREE_CODE (rhs1) == SSA_NAME
/* We only handle sign-changes or zero-extension -> & mask. */
this is sign-extension...
I think if the inner op has undefined overflow we can widen it(?). That
fixes the new testcase.
Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c (revision 274670)
+++ gcc/tree-ssa-sccvn.c (working copy)
@@ -4312,8 +4312,11 @@ visit_nary_op (tree lhs, gassign *stmt)
operation. */
if (INTEGRAL_TYPE_P (type)
&& TREE_CODE (rhs1) == SSA_NAME
- /* We only handle sign-changes or zero-extension -> & mask. */
- && ((TYPE_UNSIGNED (TREE_TYPE (rhs1))
+ /* We only handle sign-changes, zero-extension -> & mask or
+ sign-extension if we know the inner operation doesn't
+ overflow. */
+ && (((TYPE_UNSIGNED (TREE_TYPE (rhs1))
+ || TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (rhs1)))
&& TYPE_PRECISION (type) > TYPE_PRECISION (TREE_TYPE (rhs1)))
|| TYPE_PRECISION (type) == TYPE_PRECISION (TREE_TYPE (rhs1))))
{
@@ -4347,7 +4350,8 @@ visit_nary_op (tree lhs, gassign *stmt)
{
unsigned lhs_prec = TYPE_PRECISION (type);
unsigned rhs_prec = TYPE_PRECISION (TREE_TYPE (rhs1));
- if (lhs_prec == rhs_prec)
+ if (lhs_prec == rhs_prec
+ || TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (rhs1)))
{
gimple_match_op match_op (gimple_match_cond::UNCOND,
NOP_EXPR, type, ops[0]);
for the benchmark PRE inserts the this way redundant code:
Found partial redundancy for expression {nop_expr,maxIdx_31} (0012)
Inserted _72 = (long unsigned int) maxIdx_42;
in predecessor 4 (0052)
but late FRE can get rid of it again.
