[Bug target/44659] New: Combiner fails to match cmp patterns with upper 8bit register

[Bug target/44659] New: Combiner fails to match cmp patterns with upper 8bit register

[hjl dot tools at gmail dot com]

After fixing PR 44588, I got

[hjl@gnu-6 divb]$ cat umod-4.c
int
foo (unsigned char x, unsigned char y)
{
   return (x % y) != 0;
}
[hjl@gnu-6 divb]$ /export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -Os   -c -o umod-4.o umod-4.c
[hjl@gnu-6 divb]$ cat umod-4.s 
        .file   "umod-4.c"
        .text
.globl foo
        .type   foo, @function
foo:
.LFB0:
        .cfi_startproc
        movzbl  %dil, %eax
        divb    %sil
        movzbl  %ah, %eax
        testb   %al, %al
        setne   %al
        movzbl  %al, %eax
        ret

We can generate

        testb   %ah, %ah

instead of

        movzbl  %ah, %eax
        testb   %al, %al

The combine pass shows

Trying 11 -> 13: 
Failed to match this instruction:
(set (reg:CCZ 17 flags)
    (compare:CCZ (subreg:QI (lshiftrt:SI (subreg:SI (reg:HI 69) 0)
                (const_int 8 [0x8])) 0)
        (const_int 0 [0])))

with

(insn 11 10 13 2 umod-4.c:4 (set (reg:QI 67)
        (subreg:QI (zero_extract:SI (reg:HI 69)
                (const_int 8 [0x8])
                (const_int 8 [0x8])) 0)) 90 {*movqi_extzv_2_rex64}
(expr_list:REG_DEAD (reg:HI 69)
        (expr_list:REG_EQUAL (umod:QI (reg/v:QI 61 [ x ])
                (reg/v:QI 63 [ y ]))
            (nil))))

(insn 13 11 14 2 umod-4.c:4 (set (reg:CCZ 17 flags)
        (compare:CCZ (reg:QI 67)
            (const_int 0 [0]))) 0 {*cmpqi_ccno_1} (expr_list:REG_DEAD (reg:QI
67)
        (nil)))

i386.md has

(define_insn "*cmpqi_ext_2"
  [(set (reg FLAGS_REG)
        (compare
          (subreg:QI
            (zero_extract:SI
              (match_operand 0 "ext_register_operand" "Q")
              (const_int 8)
              (const_int 8)) 0)
          (match_operand:QI 1 "const0_operand" "")))]
  "ix86_match_ccmode (insn, CCNOmode)"
  "test{b}\t%h0, %h0"
  [(set_attr "type" "test")
   (set_attr "length_immediate" "0")
   (set_attr "mode" "QI")])

According to

http://gcc.gnu.org/ml/gcc-patches/2010-06/msg02477.html

(set (reg:CCZ 17 flags)
    (compare:CCZ (subreg:QI (lshiftrt:SI (subreg:SI (reg:HI 69) 0)
                (const_int 8 [0x8])) 0)
        (const_int 0 [0])))

is the standard form within combine.c. The questions are

1. Why doesn't combiner match QI cmp patterns with zero_extract?
2. Should i386.md provide QI cmp patterns with lshiftrt for
combiner?
3. Does i386.md need QI cmp patterns with zero_extract if they aren't
used by combiner?


-- 
           Summary: Combiner fails to match cmp patterns with upper 8bit
                    register
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hjl dot tools at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44659

[Bug rtl-optimization/44659] Combiner fails to match QI cmp patterns with upper 8bit register

[hjl dot tools at gmail dot com]

------- Comment #1 from hjl dot tools at gmail dot com  2010-06-24 22:41 -------
X86 backend has special support for

(zero_extract:SI (reg:M N) (const_int 8) (const_int 8))

If backend provides zero_extract, shouldn't we preserve it?


-- 

hjl dot tools at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|target                      |rtl-optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44659

[Bug rtl-optimization/44659] Combiner fails to match QI cmp patterns with upper 8bit register

[hjl dot tools at gmail dot com]

------- Comment #2 from hjl dot tools at gmail dot com  2010-06-24 22:43 -------
Created an attachment (id=20999)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=20999&action=view)
A patch

With this patch, I got

[hjl@gnu-6 divb]$ cat umod-4.c
int
foo (unsigned char x, unsigned char y)
{
   return (x % y) != 0;
}
[hjl@gnu-6 divb]$ make umod-4.s
/export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -Os -S umod-4.c
[hjl@gnu-6 divb]$ cat umod-4.s
        .file   "umod-4.c"
        .text
.globl foo
        .type   foo, @function
foo:
.LFB0:
        .cfi_startproc
        movzbl  %dil, %eax
        divb    %sil
        testw   $-256, %ax
        setne   %al
        movzbl  %al, %eax
        ret


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44659

[Bug rtl-optimization/44659] Combiner fails to match QI cmp patterns with upper 8bit register

[hjl dot tools at gmail dot com]

------- Comment #3 from hjl dot tools at gmail dot com  2010-06-25 16:43 -------
Another testcase:

[hjl@gnu-6 44659]$ cat extract-3.c
typedef struct
{
  unsigned char c1;
  unsigned char c2;
  unsigned char c3;
  unsigned char c4;
} foo_t;

int
foo (foo_t x)
{
   return x.c2 != 0;
}
[hjl@gnu-6 44659]$ make extract-3.s
/export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -Os -S extract-3.c
[hjl@gnu-6 44659]$ cat extract-3.s
        .file   "extract-3.c"
        .text
.globl foo
        .type   foo, @function
foo:
.LFB0:
        .cfi_startproc
        movl    %edi, %eax
        movzbl  %ah, %edi
        xorl    %eax, %eax
        testb   %dil, %dil
        setne   %al
        ret

movzbl  %ah, %edi
testb   %dil, %dil

can be combined into one instruction.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44659

[Bug rtl-optimization/44659] Combiner fails to match QI cmp patterns with upper 8bit register

[ebotcazou at gcc dot gnu dot org]

------- Comment #4 from ebotcazou at gcc dot gnu dot org  2010-06-29 09:24 -------
Subject: Bug 44659

Author: ebotcazou
Date: Tue Jun 29 09:24:34 2010
New Revision: 161523

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=161523
Log:
        PR rtl-optimization/44659
        * combine.c (make_compound_operation) <SUBREG>: Do not return the
        result of force_to_mode if it partially re-expanded the compound.

Added:
    trunk/gcc/testsuite/gcc.target/i386/extract-1.c
    trunk/gcc/testsuite/gcc.target/i386/extract-2.c
    trunk/gcc/testsuite/gcc.target/i386/extract-3.c
    trunk/gcc/testsuite/gcc.target/i386/extract-4.c
    trunk/gcc/testsuite/gcc.target/i386/extract-5.c
    trunk/gcc/testsuite/gcc.target/i386/extract-6.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/combine.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44659

[Bug rtl-optimization/44659] Combiner fails to match QI cmp patterns with upper 8bit register

[ebotcazou at gcc dot gnu dot org]

-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ebotcazou at gcc dot gnu dot
                   |                            |org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2010-06-29 09:24:50
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44659

[Bug rtl-optimization/44659] Combiner fails to match QI cmp patterns with upper 8bit register

[ebotcazou at gcc dot gnu dot org]

------- Comment #5 from ebotcazou at gcc dot gnu dot org  2010-07-09 10:27 -------
.


-- 

ebotcazou at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.6.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44659

[Bug rtl-optimization/44659] Combiner fails to match QI cmp patterns with upper 8bit register

[hjl at gcc dot gnu dot org]

------- Comment #6 from hjl at gcc dot gnu dot org  2010-07-10 15:35 -------
Subject: Bug 44659

Author: hjl
Date: Sat Jul 10 15:35:04 2010
New Revision: 162040

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=162040
Log:
Fix combine to match QI cmp patterns with upper 8bit register.

gcc/

2010-07-09  H.J. Lu  <hongjiu.lu@intel.com>

        Backport from mainline
        2010-06-29  Eric Botcazou  <ebotcazou@adacore.com>

        PR rtl-optimization/44659
        * combine.c (make_compound_operation) <SUBREG>: Do not return the
        result of force_to_mode if it partially re-expanded the compound.

gcc/testsuite/

2010-07-09  H.J. Lu  <hongjiu.lu@intel.com>

        Backport from mainline
        2010-06-29  H.J. Lu  <hongjiu.lu@intel.com>

        PR rtl-optimization/44659
        * gcc.target/i386/extract-1.c: New.
        * gcc.target/i386/extract-2.c: Likewise.
        * gcc.target/i386/extract-3.c: Likewise.
        * gcc.target/i386/extract-4.c: Likewise.
        * gcc.target/i386/extract-5.c: Likewise.
        * gcc.target/i386/extract-6.c: Likewise.

Added:
    branches/ix86/gcc-4_5-branch/gcc/testsuite/gcc.target/i386/extract-1.c
    branches/ix86/gcc-4_5-branch/gcc/testsuite/gcc.target/i386/extract-2.c
    branches/ix86/gcc-4_5-branch/gcc/testsuite/gcc.target/i386/extract-3.c
    branches/ix86/gcc-4_5-branch/gcc/testsuite/gcc.target/i386/extract-4.c
    branches/ix86/gcc-4_5-branch/gcc/testsuite/gcc.target/i386/extract-5.c
    branches/ix86/gcc-4_5-branch/gcc/testsuite/gcc.target/i386/extract-6.c
Modified:
    branches/ix86/gcc-4_5-branch/gcc/ChangeLog.ix86
    branches/ix86/gcc-4_5-branch/gcc/combine.c
    branches/ix86/gcc-4_5-branch/gcc/testsuite/ChangeLog.ix86


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44659