https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103271
--- Comment #8 from qinzhao at gcc dot gnu.org ---
the minimum option to repeat this failure is "-O1 -mno-strict-align".
The option "-mno-strict-align" is the one that make the difference.
For the following call to .DEFERRED_INIT:
MEM[(int[0:D.1492] *)&fb.3] = .DEFERRED_INIT (16, 1, 1);
the LHS is MEM[(int[0:D.1492] *)&fb.3].
When -mno-strict-align is NOT present, "mem_ref_refers_to_non_mem_p (lhs_base)"
return FALSE, lHS is considered as MEM, and the call is expanded through
"memset" path. No issue.
when -mno-strict-align is present, "mem_ref_refers_to_non_mem_p (lhs_base)"
return TRUE, as a result, LHS is considered to be put into a register, and then
the call is expanded through "expand_assignment" path.
The major issue during expanding through "expand_assignment" path is:
although the LHS "MEM[(int[0:D.1492] *)&fb.3]" is decided to be put into
register with TI mode, however, the TREE_TYPE of LHS is still a VLA type, such
inconsistency in IR cause the final ICE.
with the option -mno-strict-align, the IR of lhs_base is:
(gdb) call debug_tree(lhs_base)
<mem_ref 0x7ffff082bc08
type <array_type 0x7ffff082cb28
type <integer_type 0x7ffff07465e8 int sizes-gimplified public SI
size <integer_cst 0x7ffff0739bb8 constant 32>
unit-size <integer_cst 0x7ffff0739bd0 constant 4>
align:32 warn_if_not_align:0 symtab:0 alias-set 1 canonical-type
0x7ffff07465e8 precision:32 min <integer_cst 0x7ffff0739b70 -2147483648> max
<integer_cst 0x7ffff0739b88 2147483647>
pointer_to_this <pointer_type 0x7ffff074d9d8>>
sizes-gimplified type_1 BLK
size <var_decl 0x7ffff7ff0360 D.1495 type <integer_type 0x7ffff07460a8
bitsizetype>
used unsigned ignored TI t.c:8:7
size <integer_cst 0x7ffff07399c0 constant 128>
unit-size <integer_cst 0x7ffff07399d8 constant 16>
align:128 warn_if_not_align:0 context <function_decl 0x7ffff0830500
qy>>
unit-size <var_decl 0x7ffff7ff03f0 D.1496 type <integer_type
0x7ffff0746000 sizetype>
used unsigned ignored DI t.c:8:7
size <integer_cst 0x7ffff0739978 constant 64>
unit-size <integer_cst 0x7ffff0739990 constant 8>
align:64 warn_if_not_align:0 context <function_decl 0x7ffff0830500
qy>>
align:32 warn_if_not_align:0 symtab:0 alias-set -1 structural-equality
domain <integer_type 0x7ffff082ca80 type <integer_type 0x7ffff0746000
sizetype>
sizes-gimplified DI size <integer_cst 0x7ffff0739978 64> unit-size
<integer_cst 0x7ffff0739990 8>
align:64 warn_if_not_align:0 symtab:0 alias-set -1
structural-equality precision:64 min <integer_cst 0x7ffff07399a8 0> max
<var_decl 0x7ffff7ff02d0 D.1494>>
pointer_to_this <pointer_type 0x7ffff082cbd0>>
nothrow
arg:0 <addr_expr 0x7ffff082e7e0
type <pointer_type 0x7ffff082c2a0 type <array_type 0x7ffff082c1f8>
unsigned DI size <integer_cst 0x7ffff0739978 64> unit-size
<integer_cst 0x7ffff0739990 8>
align:64 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
0x7ffff082c2a0>
arg:0 <var_decl 0x7ffff7ff0990 fb.3 type <array_type 0x7ffff082c1f8>
used ignored TI t.c:8:7 size <integer_cst 0x7ffff07399c0 128>
unit-size <integer_cst 0x7ffff07399d8 16>
align:64 warn_if_not_align:0 context <function_decl 0x7ffff0830500
qy>
(reg:TI 72 [ fb.3 ])>>
arg:1 <integer_cst 0x7ffff0836fd8 type <pointer_type 0x7ffff082cbd0>
constant 0>
t.c:8:7 start: t.c:8:7 finish: t.c:8:8>
>From the above IR, we can see,
1. the base address of this mem_ref is
arg:0 <var_decl 0x7ffff7ff0990 fb.3 type <array_type 0x7ffff082c1f8>
used ignored TI t.c:8:7 size <integer_cst 0x7ffff07399c0 128>
unit-size <integer_cst 0x7ffff07399d8 16>
align:64 warn_if_not_align:0 context <function_decl 0x7ffff0830500
qy>
(reg:TI 72 [ fb.3 ])>>
which is in register of TI mode;
2. However, the TREE_TYPE of this mem_ref is still a VLA type.
when call "build_zero_cst (var_type)", the var_type is a VLA type, therefore
the ICE.
My suspicion is, -mno-strict-align applied some kind of optimization that turn
the var_decl from:
arg:0 <var_decl 0x7ffff7ff0990 fb.3 type <array_type 0x7ffff082c1f8>
used ignored BLK t.c:8:7 size <integer_cst 0x7ffff07399c0 128>
unit-size <integer_cst 0x7ffff07399d8 16>
align:128 warn_if_not_align:0 context <function_decl 0x7ffff0830500
qy>
(mem/c:BLK (plus:DI (reg/f:DI 67 virtual-stack-vars)
(const_int -16 [0xfffffffffffffff0])) [0 fb.3+0 S16 A128])>>
to:
arg:0 <var_decl 0x7ffff7ff0990 fb.3 type <array_type 0x7ffff082c1f8>
used ignored TI t.c:8:7 size <integer_cst 0x7ffff07399c0 128>
unit-size <integer_cst 0x7ffff07399d8 16>
align:64 warn_if_not_align:0 context <function_decl 0x7ffff0830500
qy>
(reg:TI 72 [ fb.3 ])>>
However, the TREE_TYPE of MEM[(int[0:D.1492] *)&fb.3] is not updated
accordingly.
