https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104839
--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
This goes wrong during fwprop1.
In #c3 testcase at -O2 in bar we have before fwprop1:
(call_insn 6 2 7 2 (parallel [
(set (reg:DI 3 3)
(call (mem:SI (symbol_ref:DI ("foo") [flags 0x3]
<function_decl 0x7fb75851b400 foo>) [0 foo S4 A8])
(const_int 0 [0])))
(use (const_int 0 [0]))
(clobber (reg:DI 96 lr))
]) "pr104839.c":10:13 755 {*call_value_localdi}
(expr_list:REG_CALL_DECL (symbol_ref:DI ("foo") [flags 0x3]
<function_decl 0x7fb75851b400 foo>)
(nil))
(expr_list (use (reg:DI 2 2))
(nil)))
(insn 7 6 8 2 (set (reg:DI 126)
(reg:DI 3 3)) "pr104839.c":10:13 670 {*movdi_internal64}
(nil))
(insn 8 7 9 2 (set (reg/v:HI 119 [ i ])
(subreg/s/u:HI (reg:DI 126) 0)) "pr104839.c":10:13 552
{*movhi_internal}
(nil))
(insn 9 8 10 2 (set (reg:SI 127)
(sign_extend:SI (reg/v:HI 119 [ i ]))) "pr104839.c":11:6 25
{*extendhisi2}
(nil))
(insn 10 9 11 2 (set (reg:SI 128)
(const_int -2 [0xfffffffffffffffe])) "pr104839.c":11:6 546
{*movsi_internal1}
(nil))
(insn 11 10 12 2 (set (reg:CC 129)
(compare:CC (reg:SI 127)
(reg:SI 128))) "pr104839.c":11:6 785 {*cmpsi_signed}
(nil))
which looks good to me, the function returns signed short and ppc64{,le} ABI
says that in that case the value is returned sign-extended into %r3.
subreg/s/u stands for promoted sign-extended.
But fwprop changes insns 8 to 11 into:
(insn 11 7 12 2 (set (reg:CC 129)
(compare:CC (subreg/s/v:SI (reg:DI 126) 0)
(const_int -2 [0xfffffffffffffffe]))) "pr104839.c":11:6 785
{*cmpsi_signed}
(nil))
where subreg/s/v stands for promoted zero-extended. That is wrong.
