Hi Uros,
Many thanks for the speedy review. Here's the revised version of the
patch incorporating all of your suggested fixes and improvements.
This has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check with no new failures. Ok for mainline?
2022-04-13 Roger Sayle <ro...@nextmovesoftware.com>
Uroš Bizjak <ubiz...@gmail.com>
gcc/ChangeLog
* config/i386/i386.md (peephole2): Transform *and_qi_maybe_si into
*andsi_2 with -Os when the instruction encoding is shorter.
gcc/testsuite/ChangeLog
* gcc.target/i386/and-1.c: New test case.
Thanks again,
Roger
--
> -----Original Message-----
> From: Uros Bizjak <ubiz...@gmail.com>
> Sent: 12 April 2022 17:37
> To: Roger Sayle <ro...@nextmovesoftware.com>
> Cc: gcc-patches@gcc.gnu.org
> Subject: Re: [x86_64 PATCH] Avoid andb %dil when optimizing for size.
>
> On Tue, Apr 12, 2022 at 5:42 PM Roger Sayle <ro...@nextmovesoftware.com>
> wrote:
> >
> >
> > This stand-alone patch avoids (-Os) regressions from a fix for PR 70321.
> >
> > The simple test case below has the unfortunate property that on x86_64
> > it is larger when compiled with -Os than when compiled with -O2.
> >
> > int foo(char x)
> > {
> > return (x & 123) != 0;
> > }
> >
> > The issue is x86's complex instruction encoding, where andb $XX,%dil
> > requires more bytes than andl $XX,%edi. This patch provides a
> > peephole2 to convert *and_qi_2_maybe_si into *andsi_2 for the problematic
> cases.
> >
> > This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> > and make -k check with no new failures. Ok for mainline?
> >
> >
> > 2022-04-12 Roger Sayle <ro...@nextmovesoftware.com>
> >
> > gcc/ChangeLog
> > * config/i386/i386.md (peephole2): Transform *and_qi_maybe_si into
> > *andsi_2 with -Os when the instruction encoding is shorter.
> >
> > gcc/testsuite/ChangeLog
> > * gcc.target/i386/and-1.c: New test case.
>
> +(define_peephole2
> + [(parallel
> + [(set (match_operand 0 "flags_reg_operand")
> + (match_operator 1 "compare_operator"
> + [(and:QI (match_operand:QI 2 "register_operand")
> + (match_operand:QI 3 "immediate_operand"))
>
> const_int_operand here, you have INTVAL accessor for this operand below.
>
> + (const_int 0)]))
> + (set (match_dup 2)
> + (and:QI (match_dup 2) (match_dup 3)))])] "TARGET_64BIT
> + && !TARGET_PARTIAL_REG_STALL
> + && optimize_insn_for_size_p ()
> + && ix86_match_ccmode (insn, CCNOmode)
> + && (INTVAL (operands[3]) & 0x80) == 0
>
> val_signbit_known_clear_p (QImode, INTVAL (operands[3]))
>
> + /* NON_Q_REG_P (operands[2]) : %sil, %dil, %bpl, %spl. */
> + && LEGACY_INT_REG_P (operands[2]) && !QI_REGNO_P (REGNO
> (operands[2]))
> + && peep2_reg_dead_p (1, operands[2])"
>
> Do we really need the above condition? Operand 2 is effectively inout operand,
> and when ANDed in SImode with zero-extended immediate, it will result in the
> same QImode value. The value outside QImode is not guaranteed without using
> strict_low_part.
>
> + [(parallel
> + [(set (match_dup 0)
> + (match_op_dup 1 [(and:SI (match_dup 2) (match_dup 3))
> + (const_int 0)]))
> + (set (match_dup 2)
> + (and:SI (match_dup 2) (match_dup 3)))])] {
> + operands[2] = gen_rtx_REG (SImode, REGNO (operands[2]));
>
> gen_lowpart (Simode, operands[2]) should work here.
>
> + operands[3] = gen_int_mode (INTVAL (operands[3]) & 0xff, SImode);
>
> No need to convert the immediate to SImode. The insn condition also
> guarantees it to be unsigned.
>
> +})
>
> Uros.
>
> > Thanks in advance,
> > Roger
> > --
> >
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index c74edd1..4ad3223 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -10140,6 +10140,35 @@
[(set_attr "type" "alu")
(set_attr "mode" "<MODE>")])
+;; On TARGET_64BIT, andb $XX,%dil is larger than andl $XX,%edi so
+;; convert *and_qi_2_maybe_si into *andsi_2 when optimizing for size.
+
+(define_peephole2
+ [(parallel
+ [(set (match_operand 0 "flags_reg_operand")
+ (match_operator 1 "compare_operator"
+ [(and:QI (match_operand:QI 2 "register_operand")
+ (match_operand:QI 3 "const_int_operand"))
+ (const_int 0)]))
+ (set (match_dup 2)
+ (and:QI (match_dup 2) (match_dup 3)))])]
+ "TARGET_64BIT
+ && !TARGET_PARTIAL_REG_STALL
+ && optimize_insn_for_size_p ()
+ && ix86_match_ccmode (insn, CCNOmode)
+ && val_signbit_known_clear_p (QImode, INTVAL (operands[3]))
+ /* NON_Q_REG_P (operands[2]) : %sil, %dil, %bpl, %spl. */
+ && LEGACY_INT_REG_P (operands[2]) && !QI_REGNO_P (REGNO (operands[2]))"
+ [(parallel
+ [(set (match_dup 0)
+ (match_op_dup 1 [(and:SI (match_dup 2) (match_dup 3))
+ (const_int 0)]))
+ (set (match_dup 2)
+ (and:SI (match_dup 2) (match_dup 3)))])]
+{
+ operands[2] = gen_lowpart (SImode, operands[2]);
+})
+
(define_expand "andqi_ext_1"
[(parallel
[(set (zero_extract:HI (match_operand:HI 0 "register_operand")
diff --git a/gcc/testsuite/gcc.target/i386/and-1.c
b/gcc/testsuite/gcc.target/i386/and-1.c
new file mode 100644
index 0000000..11890d8
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/and-1.c
@@ -0,0 +1,9 @@
+/* { dg-do compile { target { ! ia32 } } } */
+/* { dg-options "-Os" } */
+
+int foo(char x)
+{
+ return (x & 123) != 0;
+}
+
+/* { dg-final { scan-assembler-not "%dil" } } */
