Hello!
As discussed in PR 57896, calling gen_reg_rtx without populated crtl
was the cause of severe internal data corruption. The code following
/* Make sure regno_pointer_align, and regno_reg_rtx are large
enough to have an element for this pseudo reg number. */
comment is simply not prepared to handle case where
crtl->emit.regno_pointer_align_length (and reg_rtx_no) is zero. Even
when resizing the array, the allocated array size stays zero (new size
is calculated as crtl->emit.regno_pointer_align_length * 2), and
consequently
val = gen_raw_REG (mode, reg_rtx_no);
regno_reg_rtx[reg_rtx_no++] = val;
return val;
at the end of the function writes well outside the array.
IMO, the consequences of this data corruption warrant assert in
gen_reg_rtx that crtl->emit.regno_pointer_align_length is non-zero. In
case of invalid use, the compiler would ICE in a predictable way, with
a clear message where and what went wrong, instead of ICEing in random
place due to various unpredictable effects of nearby data corruption
(please see debugging troubles in the PR 57896).
I would like to propose the patch for all release branches. The
benefit of gcc_assert instead of gcc_checking_assert is in consistent
ICE (and consequently consistent bugreports) instead of a data
corruption even for the non-checking compiler. I am aware that this
assert *could* trigger some ICEs on other targets, but these will be
triggered _instead_ of internal data corruption.
2014-02-20 Uros Bizjak <ubiz...@gmail.com>
* emit-rtl.c (gen_reg_rtx): Assert that
crtl->emit.regno_pointer_align_length is non-zero.
The patch was bootstrapped and regression tested on
x86_64-pc-linux-gnu {,-m32} on 4.8 and 4.9 branch.
OK for mainline and release branches?
Uros.
Index: emit-rtl.c
===================================================================
--- emit-rtl.c (revision 207965)
+++ emit-rtl.c (working copy)
@@ -896,6 +896,9 @@ gen_reg_rtx (enum machine_mode mode)
return gen_rtx_CONCAT (mode, realpart, imagpart);
}
+ /* Do not call gen_reg_rtx with uninitialized crtl. */
+ gcc_assert (crtl->emit.regno_pointer_align_length);
+
/* Make sure regno_pointer_align, and regno_reg_rtx are large
enough to have an element for this pseudo reg number. */
