On 12/14/2021 1:18 PM, Jakub Jelinek wrote:
On Tue, Dec 14, 2021 at 10:32:21AM -0700, Jeff Law wrote:
I think the attached testcase should trigger on c6x with -mbig-endian -O2 -g
Thanks. Finally I see what's going on. c6x doesn't really need the CFA
with span > 1 (and I bet neither does armbe), the only reason why
dwf_cfa_reg is called is that the code in 13 cases just tries to compare
the CFA against dwf_cfa_reg (some_reg). And that dwf_cfa_reg on some reg
that usually isn't a CFA reg results in targetm.dwarf_register_span hook
call, which on targets like c6x or armeb and others for some registers
creates a PARALLEL with various REGs in it, then the loop with the assertion
and finally operator== which just notes that the reg is different and fails.
This seems compile time memory and time inefficient.
The following so far untested patch instead adds an extra operator== and !=
for comparison of cfa_reg with rtx, which has the most common case where it
is a different register number done early without actually invoking
dwf_cfa_reg. This means the assertion in dwf_cfa_reg can stay as is (at
least until some big endian target needs to have hard frame pointer or stack
pointer with span > 1 as well).
I've removed a different assertion there because it is redundant - dwf_regno
already has exactly that assertion in it too.
And I've included those 2 tweaks to avoid creating a REG in GC memory when
we can use {stack,hard_frame}_pointer_rtx which is already initialized to
the same REG we need by init_emit_regs.
Ok for trunk if it passes bootstrap/regtest?
2021-12-14 Jakub Jelinek <ja...@redhat.com>
PR debug/103619
* dwarf2cfi.c (dwf_cfa_reg): Remove gcc_assert.
(operator==, operator!=): New overloaded operators.
(dwarf2out_frame_debug_adjust_cfa, dwarf2out_frame_debug_cfa_offset,
dwarf2out_frame_debug_expr): Compare vars with cfa_reg type directly
with REG rtxes rather than with dwf_cfa_reg results on those REGs.
(create_cie_data): Use stack_pointer_rtx instead of
gen_rtx_REG (Pmode, STACK_POINTER_REGNUM).
(execute_dwarf2_frame): Use hard_frame_pointer_rtx instead of
gen_rtx_REG (Pmode, HARD_FRAME_POINTER_REGNUM).
So if someone is unfamiliar with the underlying issues here and needs to
twiddle dwarf2cfi, how are they supposed to know if they should compare
directly or use dwf_cfa_reg?
I'm not saying the patch is wrong, just wondering if we're setting
ourselves up for a maintenance problem going forward.
jeff
