https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67317
Uroš Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |ubizjak at gmail dot com
--- Comment #6 from Uroš Bizjak <ubizjak at gmail dot com> ---
Created attachment 36258
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36258&action=edit
Proposed patch
This patch changes expanders of carry-handling builtins to use
addqi3_cconly_overflow and canonicalizes carry hanling insn to what combine can
process:
(define_insn "addcarry<mode>"
[(set (reg:CCC FLAGS_REG)
(compare:CCC
(plus:SWI48
(plus:SWI48
(match_operator:SWI48 4 "ix86_carry_flag_operator"
[(match_operand 3 "flags_reg_operand") (const_int 0)])
(match_operand:SWI48 1 "nonimmediate_operand" "%0"))
(match_operand:SWI48 2 "nonimmediate_operand" "rm"))
(match_dup 1)))
(set (match_operand:SWI48 0 "register_operand" "=r")
(plus:SWI48 (plus:SWI48 (match_op_dup 4
[(match_dup 3) (const_int 0)])
(match_dup 1))
(match_dup 2)))]
"ix86_binary_operator_ok (PLUS, <MODE>mode, operands)"
"adc{<imodesuffix>}\t{%2, %0|%0, %2}"
[(set_attr "type" "alu")
(set_attr "use_carry" "1")
(set_attr "pent_pair" "pu")
(set_attr "mode" "<MODE>")])
and
(define_insn "subborrow<mode>"
[(set (reg:CCC FLAGS_REG)
(compare:CCC
(match_operand:SWI48 1 "nonimmediate_operand" "0")
(plus:SWI48
(match_operator:SWI48 4 "ix86_carry_flag_operator"
[(match_operand 3 "flags_reg_operand") (const_int 0)])
(match_operand:SWI48 2 "nonimmediate_operand" "rm"))))
(set (match_operand:SWI48 0 "register_operand" "=r")
(minus:SWI48 (minus:SWI48 (match_dup 1)
(match_op_dup 4
[(match_dup 3) (const_int 0)]))
(match_dup 2)))]
"ix86_binary_operator_ok (MINUS, <MODE>mode, operands)"
"sbb{<imodesuffix>}\t{%2, %0|%0, %2}"
[(set_attr "type" "alu")
(set_attr "use_carry" "1")
(set_attr "pent_pair" "pu")
(set_attr "mode" "<MODE>")])
The patch also rewrites expander to fix a bug, where carry-clobbering insns
were emitted inside carry-flag def-use chain.
For the testcase, patched gcc generates:
testcarry_u64:
addq %rdi, %rdx
adcq %rsi, %rcx
movq %rdx, %rax
xorq %rcx, %rax
ret
