How to debug a GCC segmentation fault

Configure GCC with --enable-checking. Compile it with -g -O0 so that you can use gdb.

Compile your test case with -v -da -Q.

Next, use gdb to get a stack trace:

bash$ gdb cc1
gdb> run arguments
(cc1 will stop at the segmentation fault)
gdb> where
gdb> list

Print out the values of interesting variables, e.g., the ones in the statement which got the segmentation fault. You can use the pt and pr macros from the file to display GCC data. For example, if there is a value of type tree named t, and a value of type rtx named r, you can use these commands:

gdb> source .gdbinit
gdb> print t
gdb> pt
gdb> print r
gdb> pr
gdb> pt