On Thu, Jun 29, 2017 at 10:34 AM, Richard Biener
<richard.guent...@gmail.com> wrote:
> On Thu, Jun 29, 2017 at 5:01 AM, Peter Bergner <berg...@vnet.ibm.com> wrote:
>> With the fix to PR51513 and follow on fixes for PR80707, PR80775 and PR80823,
>> we can now end up with switch statements that contain nothing but a default
>> case statement. The expand_case() function contains code that assumes we
>> have at least one non-default case statement, leading to the ICE reported
>> in the PR81194.
>>
>> This patch fixes the bug by expanding switch statements that contain only
>> a default case statement, as a GOTO to the default case's label.
>>
>> This passed bootstrap and regtesting on x86_64-linux with no regressions.
>> Ok for trunk?
>
> Ok.
>
> Btw, I'm curious -- which pass ends up with just the default case? IMHO
> it would be a cfgcleanup task but eventually we fail to run it? That is
> cleanup_control_expr_graph calls find_taken_edge () and maybe that
> doesn't handle the case where there's just the default label and thus
> the value of the switch var doesn't matter ...
To answer myself the unreachable case vanishes at
execute_cleanup_cfg_post_optimizing
via group_case_labels. find_taken_edge wouldn't handle this case either.
I am testing a patch fixing both - your patch should still go in.
Thanks,
Richard.
> Thanks,
> Richard.
>
>> Peter
>>
>> gcc/
>> PR middle-end/81194
>> * cfgexpand.c (expand_gimple_stmt_1): Handle switch statements
>> with only one label.
>> * stmt.c (expand_case): Assert NCASES is greater than one.
>>
>> gcc/testsuite/
>> PR middle-end/81194
>> * g++.dg/pr81194.C: New test.
>>
>> Index: gcc/cfgexpand.c
>> ===================================================================
>> --- gcc/cfgexpand.c (revision 249747)
>> +++ gcc/cfgexpand.c (working copy)
>> @@ -3566,7 +3566,13 @@
>> case GIMPLE_PREDICT:
>> break;
>> case GIMPLE_SWITCH:
>> - expand_case (as_a <gswitch *> (stmt));
>> + {
>> + gswitch *swtch = as_a <gswitch *> (stmt);
>> + if (gimple_switch_num_labels (swtch) == 1)
>> + expand_goto (CASE_LABEL (gimple_switch_default_label (swtch)));
>> + else
>> + expand_case (swtch);
>> + }
>> break;
>> case GIMPLE_ASM:
>> expand_asm_stmt (as_a <gasm *> (stmt));
>> Index: gcc/stmt.c
>> ===================================================================
>> --- gcc/stmt.c (revision 249747)
>> +++ gcc/stmt.c (working copy)
>> @@ -1142,8 +1142,11 @@
>> /* cleanup_tree_cfg removes all SWITCH_EXPR with their index
>> expressions being INTEGER_CST. */
>> gcc_assert (TREE_CODE (index_expr) != INTEGER_CST);
>> -
>>
>> + /* Optimization of switch statements with only one label has already
>> + occurred, so we should never see them at this point. */
>> + gcc_assert (ncases > 1);
>> +
>> do_pending_stack_adjust ();
>>
>> /* Find the default case target label. */
>> Index: gcc/testsuite/g++.dg/pr81194.C
>> ===================================================================
>> --- gcc/testsuite/g++.dg/pr81194.C (nonexistent)
>> +++ gcc/testsuite/g++.dg/pr81194.C (working copy)
>> @@ -0,0 +1,60 @@
>> +// { dg-do compile }
>> +// { dg-options "-O2 -std=c++17 -fno-exceptions" }
>> +
>> +template <class a> struct b { typedef a *c; };
>> +class e {};
>> +template <typename a> class d {
>> +public:
>> + typedef typename b<a>::c c;
>> + c begin();
>> + c end();
>> +};
>> +struct f {
>> + enum { g } h;
>> +};
>> +struct i {
>> + d<f *> j();
>> +};
>> +struct l {
>> + d<i *> k();
>> +};
>> +class ac;
>> +class o {
>> +public:
>> + o(int *, int *, int *, ac *);
>> +};
>> +class ac {
>> +public:
>> + ac(e);
>> + virtual o *ae(int *, int *, int *, int *);
>> +};
>> +class p {
>> + void af(f *m) {
>> + switch (m->h)
>> + case f::g:
>> + ag();
>> + }
>> +
>> +public:
>> + void n() {
>> + l ah;
>> + for (i *ai : ah.k())
>> + for (f *m : ai->j())
>> + af(m);
>> + }
>> + virtual void ag() { __builtin_unreachable(); }
>> +};
>> +template <typename = int> class an : o {
>> +public:
>> + an(int *, int *, int *, int *, ac *);
>> +};
>> +class q : ac {
>> +public:
>> + q() : ac([]() -> e {}()) {}
>> + o *ae(int *ap, int *aq, int *ar, int *as) { an(ap, aq, ar, as, this); }
>> +};
>> +template <typename at>
>> +an<at>::an(int *, int *aq, int *ar, int *as, ac *au) : o(aq, ar, as, au) {
>> + p().n();
>> +}
>> +void av() { new q; }
>>
