https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78016
Bug ID: 78016
Summary: REG_NOTE order is not kept during insn copy
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Keywords: ice-on-valid-code
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: jiwang at gcc dot gnu.org
CC: ebotcazou at gcc dot gnu.org, jakub at redhat dot com
Target Milestone: ---
Created attachment 39826
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39826&action=edit
keep REG_NOTE order during insn copy
I recently noticed when copying insn, GCC is actually not keeping the order of
REG_NOTEs. This seems OK for some types of REG_NOTEs, for example UNUSED,
NORETURN etc. But it seems not OK for DWARF annotation REG_NOTEs.
The reason is GCC DEARF module will do sanity check to make sure CFI rules come
from multiply paths are identical.
A B
\ /
\ /
\ /
C
For example, A and B are predecessor of C, then the following code in
"maybe_record_trace_start" in dwarf2cfi.c will do sanity check to make sure
DWARF rules come from A and B will be identical.
/* We ought to have the same state incoming to a given trace no
matter how we arrive at the trace. Anything else means we've
got some kind of optimization error. */
gcc_checking_assert (cfi_row_equal_p (cur_row, ti->beg_row));
As we don't keep the order of REG_NOTE, it's possible the final DWARF rules for
each register won't be identical.
It seems this issue is not exposed because:
* normally, only prologue and epilogue basic blocks will contain DWARF
annnocation info.
* Very few passes (bb-reorder) after pro/epi insertion pass will do insn
copy.
* DWARF sanity check happens before CFI auto deduction, normally backends
only
generate simply DWARF info. So normally we simply mark the insn as
RTX_FRAME_RELATED_P to let GCC auto-deduct the CFI annocation this happens
after the sanity check.
I came accorss the ICE when I was playing with some DWARF generation.
0x98c9f4 maybe_record_trace_start
../../gcc-svn/gcc/dwarf2cfi.c:2285
0x98cd15 create_trace_edges
../../gcc-svn/gcc/dwarf2cfi.c:2379
0x98d59e scan_trace
../../gcc-svn/gcc/dwarf2cfi.c:2593
0x98d686 create_cfi_notes
../../gcc-svn/gcc/dwarf2cfi.c:2619
0x98e172 execute_dwarf2_frame
../../gcc-svn/gcc/dwarf2cfi.c:2977
0x98ee3e execute
../../gcc-svn/gcc/dwarf2cfi.c:3457
You can reproduce this ICE by
step 1 (patch aarch64.c to generate DWARF manually)
===
Index: gcc/config/aarch64/aarch64.c
===================================================================
--- gcc/config/aarch64/aarch64.c (revision 241233)
+++ gcc/config/aarch64/aarch64.c (working copy)
@@ -2958,9 +2958,26 @@
insn = emit_insn (aarch64_gen_storewb_pair (mode, stack_pointer_rtx, reg1,
reg2, adjustment));
+#if 0
RTX_FRAME_RELATED_P (XVECEXP (PATTERN (insn), 0, 2)) = 1;
RTX_FRAME_RELATED_P (XVECEXP (PATTERN (insn), 0, 1)) = 1;
+#else
+ /* cfi_offset for reg1. */
+ rtx mem =
+ gen_rtx_MEM (Pmode, plus_constant (Pmode, stack_pointer_rtx,
-adjustment));
+ add_reg_note (insn, REG_CFA_OFFSET, gen_rtx_SET (mem, reg1));
+
+ /* cfi_offset for reg2. */
+ mem =
+ gen_rtx_MEM (Pmode,
+ plus_constant (Pmode, stack_pointer_rtx, -adjustment + 8));
+ add_reg_note (insn, REG_CFA_OFFSET, gen_rtx_SET (mem, reg2));
+
+ /* .cfi_def_cfa_offset for sp adjustment. */
+ add_reg_note (insn, REG_CFA_DEF_CFA,
+ plus_constant (Pmode, stack_pointer_rtx, -adjustment));
+ add_reg_note (insn, REG_CFA_OFFSET, gen_rtx_SET (mem, reg2));
+
+ /* .cfi_def_cfa_offset for sp adjustment. */
+ add_reg_note (insn, REG_CFA_DEF_CFA,
+ plus_constant (Pmode, stack_pointer_rtx, -adjustment));
RTX_FRAME_RELATED_P (insn) = 1;
+#endif
}
static rtx
step 2
===
./configure --target=aarch64-linux --enable-languages=c,c++
make all-gcc -j10
./gcc/cc1 ./gcc/testsuite/gcc.c-torture/execute/20031204-1.c -g -O3
-funroll-loops -fpeel-loops -ftracer -finline-functions 20031204-1.i
(please remove the #include <string.h> in the head of 20031204-1.c)
I attached a simply fix to keep REG-NOTE order during insn copy.
Any comments?
(The only relevant discussion I can find is at
https://gcc.gnu.org/ml/gcc-patches/2012-01/msg00546.html, where and when
REG_NOTE order was thinking to be not matter)
