Patchwork RFC: PR rtl-optimization/44695: [4.6 Regression] ice in simplify_subreg, at simplify-rtx.c:5117

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Submitter H.J. Lu
Date July 2, 2010, 12:35 a.m.
Message ID <AANLkTikxeh-VKv6eZewxyu33Qi_keZFj7a5CrsPcuQ7a@mail.gmail.com>
Download mbox | patch
Permalink /patch/57620/
State New
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Comments

H.J. Lu - July 2, 2010, 12:35 a.m.
On Wed, Jun 30, 2010 at 11:59 PM, Paolo Bonzini <bonzini@gnu.org> wrote:
> This is wrong. GCC may use this for a 16 to 8 bit division and cause a
> divide overflow.
>

Bernd suggested to use truncate:QI to avoid this. OK for trunk?

Thanks.
Paolo Bonzini - July 2, 2010, 6:55 a.m.
On Fri, Jul 2, 2010 at 02:35, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Wed, Jun 30, 2010 at 11:59 PM, Paolo Bonzini <bonzini@gnu.org> wrote:
>> This is wrong. GCC may use this for a 16 to 8 bit division and cause a
>> divide overflow.
>>
>
> Bernd suggested to use truncate:QI to avoid this.

Right, this is even suggested by the manual!  Thanks.  Uros or Bernd,
can you approve this?

Paolo
Uros Bizjak - July 4, 2010, 8:41 p.m.
On Fri, 2010-07-02 at 08:55 +0200, Paolo Bonzini wrote:
> On Fri, Jul 2, 2010 at 02:35, H.J. Lu <hjl.tools@gmail.com> wrote:
> > On Wed, Jun 30, 2010 at 11:59 PM, Paolo Bonzini <bonzini@gnu.org> wrote:
> >> This is wrong. GCC may use this for a 16 to 8 bit division and cause a
> >> divide overflow.
> >>
> >
> > Bernd suggested to use truncate:QI to avoid this.
> 
> Right, this is even suggested by the manual!  Thanks.  Uros or Bernd,
> can you approve this?

Yes, the patch is OK.

H.J., can you please move gen_rtx_{DIV,UDIV,MOD,UMOD} closer to the
place where they are used? It took me some scrolling up and down to see
where they are added as a REG_EQUAL. IMO, a blank line also wouldn't
hurt at that place.

Thanks,
Uros.

Patch

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 1714d50..de1d8f5 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -760,8 +760,6 @@ 
 
 ;; Used in signed and unsigned divisions.
 (define_code_iterator any_div [div udiv])
-(define_code_attr extract_code
-  [(div "SIGN_EXTRACT") (udiv "ZERO_EXTRACT")])
 
 ;; Instruction prefix for signed and unsigned operations.
 (define_code_attr sgnprefix [(sign_extend "i") (zero_extend "")
@@ -7308,9 +7306,9 @@ 
 
 ;; Divmod instructions.
 
-(define_expand "<u>divmodqi4"
+(define_expand "divmodqi4"
   [(parallel [(set (match_operand:QI 0 "register_operand" "")
-		   (any_div:QI
+		   (div:QI
 		     (match_operand:QI 1 "register_operand" "")
 		     (match_operand:QI 2 "nonimmediate_operand" "")))
 	      (set (match_operand:QI 3 "register_operand" "")
@@ -7326,31 +7324,51 @@ 
 
   /* Extend operands[1] to HImode.  Generate 8bit divide.  Result is
      in AX.  */
-  if (<extract_code> == SIGN_EXTRACT)
-    {
-      emit_insn (gen_extendqihi2 (tmp1, operands[1]));
-      emit_insn (gen_divmodhiqi3 (tmp0, tmp1, operands[2]));
+  emit_insn (gen_extendqihi2 (tmp1, operands[1]));
+  emit_insn (gen_divmodhiqi3 (tmp0, tmp1, operands[2]));
 
-      div = gen_rtx_DIV (QImode, operands[1], operands[2]);
-      mod = gen_rtx_MOD (QImode, operands[1], operands[2]);
+  div = gen_rtx_DIV (QImode, operands[1], operands[2]);
+  mod = gen_rtx_MOD (QImode, operands[1], operands[2]);
 
-      tmp1 = gen_rtx_<extract_code> (QImode, tmp0,
-				     GEN_INT (8), GEN_INT (8));
-    }
-  else
-    {
-      emit_insn (gen_zero_extendqihi2 (tmp1, operands[1]));
-      emit_insn (gen_udivmodhiqi3 (tmp0, tmp1, operands[2]));
+  /* Extract remainder from AH.  */
+  tmp1 = gen_rtx_SIGN_EXTRACT (QImode, tmp0, GEN_INT (8), GEN_INT (8));
+  insn = emit_move_insn (operands[3], tmp1);
+  set_unique_reg_note (insn, REG_EQUAL, mod);
 
-      div = gen_rtx_UDIV (QImode, operands[1], operands[2]);
-      mod = gen_rtx_UMOD (QImode, operands[1], operands[2]);
+  /* Extract quotient from AL.  */
+  insn = emit_move_insn (operands[0], gen_lowpart (QImode, tmp0));
+  set_unique_reg_note (insn, REG_EQUAL, div);
 
-      tmp1 = gen_rtx_<extract_code> (SImode, tmp0,
-				     GEN_INT (8), GEN_INT (8));
-      tmp1 = simplify_gen_subreg (QImode, tmp1, SImode, 0);
-    }
+  DONE;
+})
+
+(define_expand "udivmodqi4"
+  [(parallel [(set (match_operand:QI 0 "register_operand" "")
+		   (udiv:QI
+		     (match_operand:QI 1 "register_operand" "")
+		     (match_operand:QI 2 "nonimmediate_operand" "")))
+	      (set (match_operand:QI 3 "register_operand" "")
+		   (umod:QI (match_dup 1) (match_dup 2)))
+	      (clobber (reg:CC FLAGS_REG))])]
+  "TARGET_QIMODE_MATH"
+{
+  rtx div, mod, insn;
+  rtx tmp0, tmp1;
+  
+  tmp0 = gen_reg_rtx (HImode);
+  tmp1 = gen_reg_rtx (HImode);
+
+  /* Extend operands[1] to HImode.  Generate 8bit divide.  Result is
+     in AX.  */
+  emit_insn (gen_zero_extendqihi2 (tmp1, operands[1]));
+  emit_insn (gen_udivmodhiqi3 (tmp0, tmp1, operands[2]));
+
+  div = gen_rtx_UDIV (QImode, operands[1], operands[2]);
+  mod = gen_rtx_UMOD (QImode, operands[1], operands[2]);
 
   /* Extract remainder from AH.  */
+  tmp1 = gen_rtx_ZERO_EXTRACT (SImode, tmp0, GEN_INT (8), GEN_INT (8));
+  tmp1 = simplify_gen_subreg (QImode, tmp1, SImode, 0);
   insn = emit_move_insn (operands[3], tmp1);
   set_unique_reg_note (insn, REG_EQUAL, mod);
 
@@ -7364,15 +7382,22 @@ 
 ;; Divide AX by r/m8, with result stored in
 ;; AL <- Quotient
 ;; AH <- Remainder
+;; Change div/mod to HImode and extend the second argument to HImode
+;; so that mode of div/mod matches with mode of arguments.  Otherwise
+;; combine may fail.
 (define_insn "divmodhiqi3"
   [(set (match_operand:HI 0 "register_operand" "=a")
 	(ior:HI
 	  (ashift:HI
 	    (zero_extend:HI
-	      (mod:QI (match_operand:HI 1 "register_operand" "0")
-		      (match_operand:QI 2 "nonimmediate_operand" "qm")))
+	      (truncate:QI
+		(mod:HI (match_operand:HI 1 "register_operand" "0")
+			(sign_extend:HI
+			  (match_operand:QI 2 "nonimmediate_operand" "qm")))))
 	    (const_int 8))
-	  (zero_extend:HI (div:QI (match_dup 1) (match_dup 2)))))
+	  (zero_extend:HI
+	    (truncate:QI
+	      (div:HI (match_dup 1) (sign_extend:HI (match_dup 2)))))))
    (clobber (reg:CC FLAGS_REG))]
   "TARGET_QIMODE_MATH"
   "idiv{b}\t%2"
@@ -7384,10 +7409,14 @@ 
 	(ior:HI
 	  (ashift:HI
 	    (zero_extend:HI
-	      (umod:QI (match_operand:HI 1 "register_operand" "0")
-		       (match_operand:QI 2 "nonimmediate_operand" "qm")))
+	      (truncate:QI
+		(mod:HI (match_operand:HI 1 "register_operand" "0")
+			(zero_extend:HI
+			  (match_operand:QI 2 "nonimmediate_operand" "qm")))))
 	    (const_int 8))
-	  (zero_extend:HI (udiv:QI (match_dup 1) (match_dup 2)))))
+	  (zero_extend:HI
+	    (truncate:QI
+	      (div:HI (match_dup 1) (zero_extend:HI (match_dup 2)))))))
    (clobber (reg:CC FLAGS_REG))]
   "TARGET_QIMODE_MATH"
   "div{b}\t%2"
--- /dev/null	2010-06-16 10:11:06.602750711 -0700
+++ gcc/gcc/testsuite/gcc.dg/torture/pr44695.c	2010-06-29 11:49:12.186942482 -0700
@@ -0,0 +1,15 @@ 
+/* { dg-do compile } */
+
+typedef unsigned char uint8_t;
+
+static uint8_t
+safe_div_func_uint8_t_u_u (uint8_t ui1, uint8_t ui2)
+{
+  return ui2 ? ui2 : (ui1 / ui2);
+}
+
+int
+int81 (int x)
+{
+  return safe_div_func_uint8_t_u_u (1, 8 & x);
+}