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| author | Uros Bizjak <ubizjak@gmail.com> | 2021-04-29 22:02:00 +0200 |
|---|---|---|
| committer | Uros Bizjak <ubizjak@gmail.com> | 2021-04-29 22:03:06 +0200 |
| commit | 86403f4e6e5f72169147aca7e0d0b63e303ad5cd (patch) | |
| tree | 126a8a19c90472c45a96fb967146c23f7998d91b /gcc | |
| parent | b24d8acbfffe30f40e280f11f23adac81b1e7f0c (diff) | |
| download | gcc-86403f4e6e5f72169147aca7e0d0b63e303ad5cd.zip gcc-86403f4e6e5f72169147aca7e0d0b63e303ad5cd.tar.gz gcc-86403f4e6e5f72169147aca7e0d0b63e303ad5cd.tar.bz2 | |
i386: Optimize carry flag comparisons a bit
In ix86_int_compare, opportunistically swap operands of GTU and LEU comparisons
to emit carry flag comparison, with the expectation that the comparison will
combine to *add<mode>3_carry_0 or *sub<mode>3_carry_0 insn pattern.
Do not use ix86_expand_carry_flag_compare because this function prefers
carry flag comparisons too much - it forces the constants into registers
and/or emits additional arithmetic instructions to convert simple
comparisons into carry flag comparisons - but simply swap operands to
convert GTU and LEU comparisons into GEU and LTU ones.
Also, change the insn predicates of *add<mode>3_carry_0 and
*sub<mode>3_carry_0 insn patterns to allow more combine opportunities
with memory operands.
2021-04-29 Uroš Bizjak <ubizjak@gmail.com>
gcc/
* config/i386/i386-expand.c (ix86_expand_int_compare):
Swap operands of GTU and LEU comparison to emit carry flag comparison.
* config/i386/i386.md (*add<mode>3_carry_0): Change insn
predicate to allow more combine opportunities with memory operands.
(*sub<mode>3_carry_0): Ditto.
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/config/i386/i386-expand.c | 8 | ||||
| -rw-r--r-- | gcc/config/i386/i386.md | 4 |
2 files changed, 10 insertions, 2 deletions
diff --git a/gcc/config/i386/i386-expand.c b/gcc/config/i386/i386-expand.c index 7699062..fee4d07 100644 --- a/gcc/config/i386/i386-expand.c +++ b/gcc/config/i386/i386-expand.c @@ -2658,6 +2658,14 @@ ix86_expand_int_compare (enum rtx_code code, rtx op0, rtx op1) machine_mode cmpmode; rtx tmp, flags; + /* Swap operands to emit carry flag comparison. */ + if ((code == GTU || code == LEU) + && nonimmediate_operand (op1, VOIDmode)) + { + std::swap (op0, op1); + code = swap_condition (code); + } + cmpmode = SELECT_CC_MODE (code, op0, op1); flags = gen_rtx_REG (cmpmode, FLAGS_REG); diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md index eff189f..b7f3e36 100644 --- a/gcc/config/i386/i386.md +++ b/gcc/config/i386/i386.md @@ -6777,7 +6777,7 @@ [(match_operand 2 "flags_reg_operand") (const_int 0)]) (match_operand:SWI 1 "nonimmediate_operand" "0"))) (clobber (reg:CC FLAGS_REG))] - "ix86_unary_operator_ok (PLUS, <MODE>mode, operands)" + "!MEM_P (operands[0]) || rtx_equal_p (operands[0], operands[1])" "adc{<imodesuffix>}\t{$0, %0|%0, 0}" [(set_attr "type" "alu") (set_attr "use_carry" "1") @@ -6919,7 +6919,7 @@ (match_operator:SWI 3 "ix86_carry_flag_operator" [(match_operand 2 "flags_reg_operand") (const_int 0)]))) (clobber (reg:CC FLAGS_REG))] - "ix86_unary_operator_ok (MINUS, <MODE>mode, operands)" + "!MEM_P (operands[0]) || rtx_equal_p (operands[0], operands[1])" "sbb{<imodesuffix>}\t{$0, %0|%0, 0}" [(set_attr "type" "alu") (set_attr "use_carry" "1") |