[2/2] x86: Add cmpmemsi for -minline-all-stringops

Message ID 20200531231034.10413-3-hjl.tools@gmail.com
State New
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Series
  • x86: Add cmpmemsi for -minline-all-stringops
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Commit Message

Kees Cook via Gcc-patches May 31, 2020, 11:10 p.m.
We used to expand memcmp to "repz cmpsb" via cmpstrnsi.  It was changed
by

commit 9b0f6f5e511ca512e4faeabc81d2fd3abad9b02f
Author: Nick Clifton <nickc@redhat.com>
Date:   Fri Aug 12 16:26:11 2011 +0000

    builtins.c (expand_builtin_memcmp): Do not use cmpstrnsi pattern.

            * builtins.c (expand_builtin_memcmp): Do not use cmpstrnsi
            pattern.
            * doc/md.texi (cmpstrn): Note that the comparison stops if both
            fetched bytes are zero.
            (cmpstr): Likewise.
            (cmpmem): Note that the comparison does not stop if both of the
            fetched bytes are zero.

Duplicate the cmpstrn pattern for cmpmem and expand cmpmem to "repz cmpsb"
for -minline-all-stringops.  The only difference is that the length
argument of cmpmem is guaranteed to be less than or equal to lengths of
2 memory areas.

gcc/

	PR target/95151
	* config/i386/i386-expand.c (ix86_expand_cmpstrn_or_cmpmem): New
	function.
	* config/i386/i386-protos.h (ix86_expand_cmpstrn_or_cmpmem): New
	prototype.
	* config/i386/i386.md (cmpmemsi): New pattern.

gcc/testsuite/

	PR target/95151
	* gcc.target/i386/pr95151-1.c: New test.
	* gcc.target/i386/pr95151-2.c: Likewise.
	* gcc.target/i386/pr95151-3.c: Likewise.
	* gcc.target/i386/pr95151-4.c: Likewise.
---
 gcc/config/i386/i386-expand.c             | 84 +++++++++++++++++++++++
 gcc/config/i386/i386-protos.h             |  1 +
 gcc/config/i386/i386.md                   | 84 ++++++-----------------
 gcc/testsuite/gcc.target/i386/pr95151-1.c | 17 +++++
 gcc/testsuite/gcc.target/i386/pr95151-2.c | 10 +++
 gcc/testsuite/gcc.target/i386/pr95151-3.c | 18 +++++
 gcc/testsuite/gcc.target/i386/pr95151-4.c | 11 +++
 7 files changed, 162 insertions(+), 63 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr95151-1.c
 create mode 100644 gcc/testsuite/gcc.target/i386/pr95151-2.c
 create mode 100644 gcc/testsuite/gcc.target/i386/pr95151-3.c
 create mode 100644 gcc/testsuite/gcc.target/i386/pr95151-4.c

-- 
2.26.2

Comments

Kees Cook via Gcc-patches June 1, 2020, 10:19 a.m. | #1
On Sun, 31 May 2020, H.J. Lu via Gcc-patches wrote:

> --- a/gcc/config/i386/i386-expand.c

> +++ b/gcc/config/i386/i386-expand.c

> @@ -7656,6 +7656,90 @@ ix86_expand_set_or_cpymem (rtx dst, rtx src, rtx count_exp, rtx val_exp,

>    return true;

>  }

>  

> +/* Expand cmpstrn or memcmp.  */

> +

> +bool

> +ix86_expand_cmpstrn_or_cmpmem (rtx result, rtx src1, rtx src2,

> +			       rtx length, rtx align, bool is_cmpstrn)

> +{

> +  if (optimize_insn_for_size_p () && !TARGET_INLINE_ALL_STRINGOPS)

> +    return false;

> +

> +  /* Can't use this if the user has appropriated ecx, esi or edi.  */

> +  if (fixed_regs[CX_REG] || fixed_regs[SI_REG] || fixed_regs[DI_REG])

> +    return false;

> +

> +  if (is_cmpstrn)

> +    {

> +      /* For strncmp, length is the maximum length, which can be larger

> +	 than actual string lengths.  We can expand the cmpstrn pattern

> +	 to "repz cmpsb" only if one of the strings is a constant so

> +	 that expand_builtin_strncmp() can write the length argument to

> +	 be the minimum of the const string length and the actual length

> +	 argument.  Otherwise, "repz cmpsb" may pass the 0 byte.  */

> +      tree t1 = MEM_EXPR (src1);

> +      tree t2 = MEM_EXPR (src2);

> +      if (!((t1 && TREE_CODE (t1) == MEM_REF

> +	     && TREE_CODE (TREE_OPERAND (t1, 0)) == ADDR_EXPR

> +	     && (TREE_CODE (TREE_OPERAND (TREE_OPERAND (t1, 0), 0))

> +		 == STRING_CST))

> +	    || (t2 && TREE_CODE (t2) == MEM_REF

> +		&& TREE_CODE (TREE_OPERAND (t2, 0)) == ADDR_EXPR

> +		&& (TREE_CODE (TREE_OPERAND (TREE_OPERAND (t2, 0), 0))

> +		    == STRING_CST))))

> +	return false;

> +    }

> +  else

> +    {

> +      /* Expand memcmp to "repz cmpsb" only for -minline-all-stringops

> +	 since "repz cmpsb" can be much slower than memcmp function

> +	 implemented with vector instructions, see

> +

> +	 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43052

> +       */

> +      if (!TARGET_INLINE_ALL_STRINGOPS)

> +	return false;

> +    }


This check seems to be misplaced, "rep cmps" is slower than either memcmp or
strcmp. The test for TARGET_INLINE_ALL_STRINGOPS should happen regardless of
is_cmpstrn, so it should go earlier in the function.

Alexander
Kees Cook via Gcc-patches June 1, 2020, 12:21 p.m. | #2
On Mon, Jun 1, 2020 at 3:19 AM Alexander Monakov <amonakov@ispras.ru> wrote:
>

> On Sun, 31 May 2020, H.J. Lu via Gcc-patches wrote:

>

> > --- a/gcc/config/i386/i386-expand.c

> > +++ b/gcc/config/i386/i386-expand.c

> > @@ -7656,6 +7656,90 @@ ix86_expand_set_or_cpymem (rtx dst, rtx src, rtx count_exp, rtx val_exp,

> >    return true;

> >  }

> >

> > +/* Expand cmpstrn or memcmp.  */

> > +

> > +bool

> > +ix86_expand_cmpstrn_or_cmpmem (rtx result, rtx src1, rtx src2,

> > +                            rtx length, rtx align, bool is_cmpstrn)

> > +{

> > +  if (optimize_insn_for_size_p () && !TARGET_INLINE_ALL_STRINGOPS)

> > +    return false;

> > +

> > +  /* Can't use this if the user has appropriated ecx, esi or edi.  */

> > +  if (fixed_regs[CX_REG] || fixed_regs[SI_REG] || fixed_regs[DI_REG])

> > +    return false;

> > +

> > +  if (is_cmpstrn)

> > +    {

> > +      /* For strncmp, length is the maximum length, which can be larger

> > +      than actual string lengths.  We can expand the cmpstrn pattern

> > +      to "repz cmpsb" only if one of the strings is a constant so

> > +      that expand_builtin_strncmp() can write the length argument to

> > +      be the minimum of the const string length and the actual length

> > +      argument.  Otherwise, "repz cmpsb" may pass the 0 byte.  */

> > +      tree t1 = MEM_EXPR (src1);

> > +      tree t2 = MEM_EXPR (src2);

> > +      if (!((t1 && TREE_CODE (t1) == MEM_REF

> > +          && TREE_CODE (TREE_OPERAND (t1, 0)) == ADDR_EXPR

> > +          && (TREE_CODE (TREE_OPERAND (TREE_OPERAND (t1, 0), 0))

> > +              == STRING_CST))

> > +         || (t2 && TREE_CODE (t2) == MEM_REF

> > +             && TREE_CODE (TREE_OPERAND (t2, 0)) == ADDR_EXPR

> > +             && (TREE_CODE (TREE_OPERAND (TREE_OPERAND (t2, 0), 0))

> > +                 == STRING_CST))))

> > +     return false;

> > +    }

> > +  else

> > +    {

> > +      /* Expand memcmp to "repz cmpsb" only for -minline-all-stringops

> > +      since "repz cmpsb" can be much slower than memcmp function

> > +      implemented with vector instructions, see

> > +

> > +      https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43052

> > +       */

> > +      if (!TARGET_INLINE_ALL_STRINGOPS)

> > +     return false;

> > +    }

>

> This check seems to be misplaced, "rep cmps" is slower than either memcmp or

> strcmp. The test for TARGET_INLINE_ALL_STRINGOPS should happen regardless of

> is_cmpstrn, so it should go earlier in the function.

>


My patch doesn't change strncmp at all.   I opened:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95458


-- 
H.J.

Patch

diff --git a/gcc/config/i386/i386-expand.c b/gcc/config/i386/i386-expand.c
index 270585decb2..9e27564037b 100644
--- a/gcc/config/i386/i386-expand.c
+++ b/gcc/config/i386/i386-expand.c
@@ -7656,6 +7656,90 @@  ix86_expand_set_or_cpymem (rtx dst, rtx src, rtx count_exp, rtx val_exp,
   return true;
 }
 
+/* Expand cmpstrn or memcmp.  */
+
+bool
+ix86_expand_cmpstrn_or_cmpmem (rtx result, rtx src1, rtx src2,
+			       rtx length, rtx align, bool is_cmpstrn)
+{
+  if (optimize_insn_for_size_p () && !TARGET_INLINE_ALL_STRINGOPS)
+    return false;
+
+  /* Can't use this if the user has appropriated ecx, esi or edi.  */
+  if (fixed_regs[CX_REG] || fixed_regs[SI_REG] || fixed_regs[DI_REG])
+    return false;
+
+  if (is_cmpstrn)
+    {
+      /* For strncmp, length is the maximum length, which can be larger
+	 than actual string lengths.  We can expand the cmpstrn pattern
+	 to "repz cmpsb" only if one of the strings is a constant so
+	 that expand_builtin_strncmp() can write the length argument to
+	 be the minimum of the const string length and the actual length
+	 argument.  Otherwise, "repz cmpsb" may pass the 0 byte.  */
+      tree t1 = MEM_EXPR (src1);
+      tree t2 = MEM_EXPR (src2);
+      if (!((t1 && TREE_CODE (t1) == MEM_REF
+	     && TREE_CODE (TREE_OPERAND (t1, 0)) == ADDR_EXPR
+	     && (TREE_CODE (TREE_OPERAND (TREE_OPERAND (t1, 0), 0))
+		 == STRING_CST))
+	    || (t2 && TREE_CODE (t2) == MEM_REF
+		&& TREE_CODE (TREE_OPERAND (t2, 0)) == ADDR_EXPR
+		&& (TREE_CODE (TREE_OPERAND (TREE_OPERAND (t2, 0), 0))
+		    == STRING_CST))))
+	return false;
+    }
+  else
+    {
+      /* Expand memcmp to "repz cmpsb" only for -minline-all-stringops
+	 since "repz cmpsb" can be much slower than memcmp function
+	 implemented with vector instructions, see
+
+	 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43052
+       */
+      if (!TARGET_INLINE_ALL_STRINGOPS)
+	return false;
+    }
+
+  rtx addr1 = copy_addr_to_reg (XEXP (src1, 0));
+  rtx addr2 = copy_addr_to_reg (XEXP (src2, 0));
+  if (addr1 != XEXP (src1, 0))
+    src1 = replace_equiv_address_nv (src1, addr1);
+  if (addr2 != XEXP (src2, 0))
+    src2 = replace_equiv_address_nv (src2, addr2);
+
+  /* NB: Make a copy of the data length to avoid changing the original
+     data length by cmpstrnqi patterns.  */
+  length = ix86_zero_extend_to_Pmode (length);
+  rtx lengthreg = gen_reg_rtx (Pmode);
+  emit_move_insn (lengthreg, length);
+
+  /* If we are testing strict equality, we can use known alignment to
+     good advantage.  This may be possible with combine, particularly
+     once cc0 is dead.  */
+  if (CONST_INT_P (length))
+    {
+      if (length == const0_rtx)
+	{
+	  emit_move_insn (result, const0_rtx);
+	  return true;
+	}
+      emit_insn (gen_cmpstrnqi_nz_1 (addr1, addr2, lengthreg, align,
+				     src1, src2));
+    }
+  else
+    {
+      emit_insn (gen_cmp_1 (Pmode, lengthreg, lengthreg));
+      emit_insn (gen_cmpstrnqi_1 (addr1, addr2, lengthreg, align,
+				  src1, src2));
+    }
+
+  rtx out = gen_lowpart (QImode, result);
+  emit_insn (gen_cmpintqi (out));
+  emit_move_insn (result, gen_rtx_SIGN_EXTEND (SImode, out));
+
+  return true;
+}
 
 /* Expand the appropriate insns for doing strlen if not just doing
    repnz; scasb
diff --git a/gcc/config/i386/i386-protos.h b/gcc/config/i386/i386-protos.h
index 39fcaa0ad5f..238aa650b61 100644
--- a/gcc/config/i386/i386-protos.h
+++ b/gcc/config/i386/i386-protos.h
@@ -71,6 +71,7 @@  extern int avx_vperm2f128_parallel (rtx par, machine_mode mode);
 extern bool ix86_expand_strlen (rtx, rtx, rtx, rtx);
 extern bool ix86_expand_set_or_cpymem (rtx, rtx, rtx, rtx, rtx, rtx,
 				       rtx, rtx, rtx, rtx, bool);
+extern bool ix86_expand_cmpstrn_or_cmpmem (rtx, rtx, rtx, rtx, rtx, bool);
 
 extern bool constant_address_p (rtx);
 extern bool legitimate_pic_operand_p (rtx);
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index c2de1bdaf42..dec8dd17168 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -17777,6 +17777,22 @@  (define_insn "*rep_stosqi"
 	  (const_string "*")))
    (set_attr "mode" "QI")])
 
+(define_expand "cmpmemsi"
+  [(set (match_operand:SI 0 "register_operand" "")
+        (compare:SI (match_operand:BLK 1 "memory_operand" "")
+                    (match_operand:BLK 2 "memory_operand" "") ) )
+   (use (match_operand 3 "general_operand"))
+   (use (match_operand 4 "immediate_operand"))]
+  ""
+{
+  if (ix86_expand_cmpstrn_or_cmpmem (operands[0], operands[1],
+				     operands[2], operands[3],
+				     operands[4], false))
+    DONE;
+  else
+    FAIL;
+})
+
 (define_expand "cmpstrnsi"
   [(set (match_operand:SI 0 "register_operand")
 	(compare:SI (match_operand:BLK 1 "general_operand")
@@ -17785,70 +17801,12 @@  (define_expand "cmpstrnsi"
    (use (match_operand 4 "immediate_operand"))]
   ""
 {
-  rtx addr1, addr2, countreg, align, out;
-
-  if (optimize_insn_for_size_p () && !TARGET_INLINE_ALL_STRINGOPS)
-    FAIL;
-
-  /* Can't use this if the user has appropriated ecx, esi or edi.  */
-  if (fixed_regs[CX_REG] || fixed_regs[SI_REG] || fixed_regs[DI_REG])
-    FAIL;
-
-  /* One of the strings must be a constant.  If so, expand_builtin_strncmp()
-     will have rewritten the length arg to be the minimum of the const string
-     length and the actual length arg.  If both strings are the same and
-     shorter than the length arg, repz cmpsb will not stop at the 0 byte and
-     will incorrectly base the results on chars past the 0 byte.  */
-  tree t1 = MEM_EXPR (operands[1]);
-  tree t2 = MEM_EXPR (operands[2]);
-  if (!((t1 && TREE_CODE (t1) == MEM_REF
-         && TREE_CODE (TREE_OPERAND (t1, 0)) == ADDR_EXPR
-         && TREE_CODE (TREE_OPERAND (TREE_OPERAND (t1, 0), 0)) == STRING_CST)
-      || (t2 && TREE_CODE (t2) == MEM_REF
-          && TREE_CODE (TREE_OPERAND (t2, 0)) == ADDR_EXPR
-          && TREE_CODE (TREE_OPERAND (TREE_OPERAND (t2, 0), 0)) == STRING_CST)))
-    FAIL;
-
-  addr1 = copy_addr_to_reg (XEXP (operands[1], 0));
-  addr2 = copy_addr_to_reg (XEXP (operands[2], 0));
-  if (addr1 != XEXP (operands[1], 0))
-    operands[1] = replace_equiv_address_nv (operands[1], addr1);
-  if (addr2 != XEXP (operands[2], 0))
-    operands[2] = replace_equiv_address_nv (operands[2], addr2);
-
-  /* NB: Make a copy of the data length to avoid changing the original
-     data length by cmpstrnqi patterns.  */
-  rtx count = ix86_zero_extend_to_Pmode (operands[3]);
-  countreg = gen_reg_rtx (Pmode);
-  emit_move_insn (countreg, count);
-
-  /* %%% Iff we are testing strict equality, we can use known alignment
-     to good advantage.  This may be possible with combine, particularly
-     once cc0 is dead.  */
-  align = operands[4];
-
-  if (CONST_INT_P (operands[3]))
-    {
-      if (operands[3] == const0_rtx)
-	{
-	  emit_move_insn (operands[0], const0_rtx);
-	  DONE;
-	}
-      emit_insn (gen_cmpstrnqi_nz_1 (addr1, addr2, countreg, align,
-				     operands[1], operands[2]));
-    }
+  if (ix86_expand_cmpstrn_or_cmpmem (operands[0], operands[1],
+				     operands[2], operands[3],
+				     operands[4], true))
+    DONE;
   else
-    {
-      emit_insn (gen_cmp_1 (Pmode, countreg, countreg));
-      emit_insn (gen_cmpstrnqi_1 (addr1, addr2, countreg, align,
-				  operands[1], operands[2]));
-    }
-
-  out = gen_lowpart (QImode, operands[0]);
-  emit_insn (gen_cmpintqi (out));
-  emit_move_insn (operands[0], gen_rtx_SIGN_EXTEND (SImode, out));
-
-  DONE;
+    FAIL;
 })
 
 ;; Produce a tri-state integer (-1, 0, 1) from condition codes.
diff --git a/gcc/testsuite/gcc.target/i386/pr95151-1.c b/gcc/testsuite/gcc.target/i386/pr95151-1.c
new file mode 100644
index 00000000000..54a7510042a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr95151-1.c
@@ -0,0 +1,17 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -minline-all-stringops" } */
+
+struct foo
+{
+  char array[257];
+};
+
+extern struct foo x;
+
+int
+func (struct foo i)
+{
+  return __builtin_memcmp (&x, &i, sizeof (x)) ? 1 : 2;
+}
+
+/* { dg-final { scan-assembler-not "call\[\\t \]*_?memcmp" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr95151-2.c b/gcc/testsuite/gcc.target/i386/pr95151-2.c
new file mode 100644
index 00000000000..8f9d8ee1bf4
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr95151-2.c
@@ -0,0 +1,10 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -minline-all-stringops" } */
+
+int
+func (void *d, void *s, unsigned int l)
+{
+  return __builtin_memcmp (d, s, l) ? 1 : 2;
+}
+
+/* { dg-final { scan-assembler-not "call\[\\t \]*_?memcmp" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr95151-3.c b/gcc/testsuite/gcc.target/i386/pr95151-3.c
new file mode 100644
index 00000000000..14cbdec4c93
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr95151-3.c
@@ -0,0 +1,18 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -msse2 -mno-inline-all-stringops" } */
+
+struct foo
+{
+  char array[257];
+};
+
+extern struct foo x;
+
+int
+func (struct foo i)
+{
+  return __builtin_memcmp (&x, &i, sizeof (x)) ? 1 : 2;
+}
+
+/* { dg-final { scan-assembler "call\[\\t \]*_?memcmp" } } */
+/* { dg-final { scan-assembler-not "cmpsb" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr95151-4.c b/gcc/testsuite/gcc.target/i386/pr95151-4.c
new file mode 100644
index 00000000000..c93b2b60c5b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr95151-4.c
@@ -0,0 +1,11 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -msse2 -mno-inline-all-stringops" } */
+
+int
+func (void *d, void *s, unsigned int l)
+{
+  return __builtin_memcmp (d, s, l) ? 1 : 2;
+}
+
+/* { dg-final { scan-assembler "call\[\\t \]*_?memcmp" } } */
+/* { dg-final { scan-assembler-not "cmpsb" } } */