https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84136
--- Comment #4 from David Malcolm ---
Author: dmalcolm
Date: Fri Feb 9 01:07:11 2018
New Revision: 257509
URL: https://gcc.gnu.org/viewcvs?rev=257509=gcc=rev
Log:
Fix ICE in find_taken_edge_computed_goto (PR 84136)
PR 84136 reports an ICE within sccvn_dom_walker when handling a
C/C++ source file that overuses the labels-as-values extension.
The code in question stores a jump label into a global, and then
jumps to it from another function, which ICEs after inlining:
void* a;
void foo() {
if ((a = &))
return;
l:;
}
int main() {
foo();
goto *a;
return 0;
}
This appears to be far beyond what we claim to support in this
extension - but we shouldn't ICE.
What's happening is that, after inlining, we have usage of a *copy*
of the label, which optimizes away the if-return logic, turning it
into an infinite loop.
On entry to the sccvn_dom_walker we have this gimple:
main ()
{
void * a.0_1;
[count: 0]:
a =
[count: 0]:
l:
a.0_1 = a;
goto a.0_1;
}
and:
edge taken = find_taken_edge (bb, vn_valueize (val));
reasonably valueizes the:
goto a.0_1;
after the:
a =
a.0_1 = a;
as if it were:
goto *
find_taken_edge_computed_goto then has:
2380 dest = label_to_block (val);
2381 if (dest)
2382{
2383 e = find_edge (bb, dest);
2384 gcc_assert (e != NULL);
2385}
which locates dest as a self-jump from block 3 back to itself.
However, the find_edge call returns NULL - it has a predecessor edge
from block 2, but no successor edges.
Hence the assertion fails and we ICE.
A successor edge from the computed goto could have been created by
make_edges if the label stmt had been in the function, but make_edges
only looks in the current function when handling computed gotos, and
the label only appeared after inlining.
The following patch removes the assertion, fixing the ICE.
gcc/testsuite/ChangeLog:
PR tree-optimization/84136
* gcc.c-torture/compile/pr84136.c: New test.
gcc/ChangeLog:
PR tree-optimization/84136
* tree-cfg.c (find_taken_edge_computed_goto): Remove assertion
that the result of find_edge is non-NULL.
Added:
trunk/gcc/testsuite/gcc.c-torture/compile/pr84136.c
Modified:
trunk/gcc/ChangeLog
trunk/gcc/testsuite/ChangeLog
trunk/gcc/tree-cfg.c
