Hi!
On the following testcase info.final_bb has only one PHI, the virtual one,
so info.phi_count is 0. For info.phi_count == 0, we don't really create any
arrays etc.; just returning early (before create_temp_arrays) would work,
but would leave the useless GIMPLE_SWITCH in the IL and it would take many
passes to optimize it properly. We know that all but the default: bbs are
really empty and the default: can do something arbitrary, if all the ranges
are consecutive, it is better to just let gen_inbound_check do its work
and convert the switch into if (cond) { former_default_bb }.
All but build_constructors function can handle 0 info.phi_count, but
build_constructors can't, on the other side doesn't need to do anything
if it is 0.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2018-03-07 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/84740
* tree-switch-conversion.c (process_switch): Call build_constructors
only if info.phi_count is non-zero.
* gcc.dg/torture/pr84740.c: New test.
--- gcc/tree-switch-conversion.c.jj 2018-01-09 08:58:15.000000000 +0100
+++ gcc/tree-switch-conversion.c 2018-03-07 12:03:42.228246408 +0100
@@ -1563,7 +1563,8 @@ process_switch (gswitch *swtch)
gather_default_values (info.default_case_nonstandard
? gimple_switch_label (swtch, 1)
: gimple_switch_default_label (swtch), &info);
- build_constructors (swtch, &info);
+ if (info.phi_count)
+ build_constructors (swtch, &info);
build_arrays (swtch, &info); /* Build the static arrays and assignments. */
gen_inbound_check (swtch, &info); /* Build the bounds check. */
--- gcc/testsuite/gcc.dg/torture/pr84740.c.jj 2018-03-07 12:13:02.153271986
+0100
+++ gcc/testsuite/gcc.dg/torture/pr84740.c 2018-03-07 12:12:42.643270368
+0100
@@ -0,0 +1,24 @@
+/* PR tree-optimization/84740 */
+
+void
+frobulate_for_gcc (unsigned int v)
+{
+ const char *s;
+ switch (v)
+ {
+ case 0:
+ s = "foo";
+ break;
+ case 1:
+ s = "bar";
+ break;
+ case 2:
+ s = "spam";
+ break;
+ default:
+ s = (const char *) 0;
+ break;
+ }
+ if (!s)
+ __builtin_printf ("%s\n", s);
+}
Jakub
