https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79444
Bug ID: 79444
Summary: Inconsistent use of DW_OP_piece for vector registers
on s390x
Product: gcc
Version: 7.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: arnez at linux dot vnet.ibm.com
Target Milestone: ---
GCC emits DW_OP_piece for vector registers on s390x in (at least) two
different incompatible ways:
(1) When describing a float field in a structure that was optimized into a
floating-point register:
extern void do_something (float a, float b, float s, float p);
void foo (float a, float b)
{
struct { float a; float b; } s = { a, b };
do_something (a, b, s.a + s.b, s.a * s.b);
}
Compiling the above with "gcc -march=z13 -O3 -g" yields a location list
for foo's variable 's' with an entry like this:
(DW_OP_reg16 (f0); DW_OP_piece: 4; DW_OP_reg17 (f2); DW_OP_piece: 4)
Here the piece operations refer to the *upper* bytes of the floating-point
registers f0 and f2 (aka v0 and v2).
(2) When describing an __int128 bit field that was optimized into a vector
register:
extern void do_something (__int128);
void foo (__int128 x, __int128 y)
{
struct {
unsigned __int128 p: 32;
unsigned __int128 a: 96;
} w = {0, x};
do_something (w.a + y);
}
Compiling the above code with "gcc -march=z13 -O3 -g" yields a location
list for foo's variable 'w' with an entry like this:
(DW_OP_lit0; DW_OP_stack_value; DW_OP_piece: 4; DW_OP_reg16 (f0);
DW_OP_piece: 12)
And here the latter piece operation refers to the *lower* bytes of the vector
register v0.
