[PATCH] MIPS: remove comparison modes in branches + combiner fix

[Adam Nemet <anemet at sonic dot net>]

Jim Wilson writes:
> Yes, it looks like fixing the combiner problem would make it
> possible to remove the mistaken mode checks.

Jim,

Thanks again for confirming this.  Below is the patch for the combine
issue(s) and the actual backend change.

In turns out I had to fix another missed TRULY_NOOP_TRUNCATION check
in combine for the testcase to work.

What I mentioned in my previous email too is that simplify_comparison
<AND> transforms this

  (ne:DI (and:DI (reg:DI 4) (const_int 0xffffffff)) (const_int 0))

into this:

  (ne:DI (reg:SI 4) (const_int 0))

After I added the check for TRULY_NOOP_TRUNCATION I still got the same
wrong assembly output because there is a similar transformation in
make_compound_operation <AND>.  make_extraction is called from there
to extract the lower 16 bits and it returns a subreg.  So for the AND
part of the expression we get:

  (zero_extend:DI (reg:SI 4))

Strictly speaking this is already incorrect but it still works on
MIPS.  The actual wrong code we get when simplify_comparison
<ZERO_EXTEND> removes the zero-extension since it is unnecessary when
comparing to zero.

I changed make_extraction to only return a subreg is
TRULY_NOOP_TRUNCATION permits it.

Regression-tested on mips64-elf.  Tested and bootstrapped on
i686-pc-linux-gnu.

Is it OK to apply?

Adam

        * gcc.c-torture/execute/20051213-1.c: New test. 


        * combine.c (make_extraction): Check TRULY_NOOP_TRUNCATION before 
        start using a subreg. 
        (simplify_comparison <AND>): Likewise. 
 
        * config/mips/mips.md (*branch_zero<mode>, 
        *branch_zero<mode>_inverted, *branch_equality<mode>, 
        *branch_equality<mode>_inverted, *branch_equality<mode>_mips16): 
        Remove mode check from comparisons. 

Index: gcc/testsuite/gcc.c-torture/execute/20051213-1.c
===================================================================
--- gcc/testsuite/gcc.c-torture/execute/20051213-1.c	(revision 0)
+++ gcc/testsuite/gcc.c-torture/execute/20051213-1.c	(revision 0)
@@ -0,0 +1,17 @@
+void abort ();
+
+void
+f (long long a)
+{
+  if ((a & 0xffffffffLL) != 0)
+    abort ();
+}
+
+long long a = 0x1234567800000000LL;
+
+int
+main ()
+{
+  f (a);
+  return 0;
+}
Index: gcc/combine.c
===================================================================
--- gcc/combine.c	(revision 108488)
+++ gcc/combine.c	(working copy)
@@ -6356,7 +6356,9 @@ make_extraction (enum machine_mode mode,
 	}
       else if (REG_P (inner))
 	{
-	  if (tmode != inner_mode)
+	  if (tmode != inner_mode
+	      && TRULY_NOOP_TRUNCATION (GET_MODE_BITSIZE (tmode),
+					GET_MODE_BITSIZE (inner_mode)))
 	    {
 	      /* We can't call gen_lowpart in a DEST since we
 		 always want a SUBREG (see below) and it would sometimes
@@ -10547,7 +10549,9 @@ simplify_comparison (enum rtx_code code,
 				   & GET_MODE_MASK (mode))
 				  + 1)) >= 0
 	      && const_op >> i == 0
-	      && (tmode = mode_for_size (i, MODE_INT, 1)) != BLKmode)
+	      && (tmode = mode_for_size (i, MODE_INT, 1)) != BLKmode
+	      && TRULY_NOOP_TRUNCATION (GET_MODE_BITSIZE (tmode),
+					GET_MODE_BITSIZE (GET_MODE (op0))))
 	    {
 	      op0 = gen_lowpart (tmode, XEXP (op0, 0));
 	      continue;
Index: gcc/config/mips/mips.md
===================================================================
--- gcc/config/mips/mips.md	(revision 108488)
+++ gcc/config/mips/mips.md	(working copy)
@@ -4291,9 +4291,9 @@ (define_insn "branch_fp_inverted"
 (define_insn "*branch_zero<mode>"
   [(set (pc)
 	(if_then_else
-	 (match_operator:GPR 0 "comparison_operator"
-			     [(match_operand:GPR 2 "register_operand" "d")
-			      (const_int 0)])
+	 (match_operator 0 "comparison_operator"
+			 [(match_operand:GPR 2 "register_operand" "d")
+			  (const_int 0)])
 	 (label_ref (match_operand 1 "" ""))
 	 (pc)))]
   "!TARGET_MIPS16"
@@ -4311,9 +4311,9 @@ (define_insn "*branch_zero<mode>"
 (define_insn "*branch_zero<mode>_inverted"
   [(set (pc)
 	(if_then_else
-	 (match_operator:GPR 0 "comparison_operator"
-			     [(match_operand:GPR 2 "register_operand" "d")
-			      (const_int 0)])
+	 (match_operator 0 "comparison_operator"
+			 [(match_operand:GPR 2 "register_operand" "d")
+			  (const_int 0)])
 	 (pc)
 	 (label_ref (match_operand 1 "" ""))))]
   "!TARGET_MIPS16"
@@ -4333,9 +4333,9 @@ (define_insn "*branch_zero<mode>_inverte
 (define_insn "*branch_equality<mode>"
   [(set (pc)
 	(if_then_else
-	 (match_operator:GPR 0 "equality_operator"
-			     [(match_operand:GPR 2 "register_operand" "d")
-			      (match_operand:GPR 3 "register_operand" "d")])
+	 (match_operator 0 "equality_operator"
+			 [(match_operand:GPR 2 "register_operand" "d")
+			  (match_operand:GPR 3 "register_operand" "d")])
 	 (label_ref (match_operand 1 "" ""))
 	 (pc)))]
   "!TARGET_MIPS16"
@@ -4353,9 +4353,9 @@ (define_insn "*branch_equality<mode>"
 (define_insn "*branch_equality<mode>_inverted"
   [(set (pc)
 	(if_then_else
-	 (match_operator:GPR 0 "equality_operator"
-			     [(match_operand:GPR 2 "register_operand" "d")
-			      (match_operand:GPR 3 "register_operand" "d")])
+	 (match_operator 0 "equality_operator"
+			 [(match_operand:GPR 2 "register_operand" "d")
+			  (match_operand:GPR 3 "register_operand" "d")])
 	 (pc)
 	 (label_ref (match_operand 1 "" ""))))]
   "!TARGET_MIPS16"
@@ -4375,9 +4375,9 @@ (define_insn "*branch_equality<mode>_inv
 (define_insn "*branch_equality<mode>_mips16"
   [(set (pc)
 	(if_then_else
-	 (match_operator:GPR 0 "equality_operator"
-			     [(match_operand:GPR 1 "register_operand" "d,t")
-			      (const_int 0)])
+	 (match_operator 0 "equality_operator"
+			 [(match_operand:GPR 1 "register_operand" "d,t")
+			  (const_int 0)])
 	 (match_operand 2 "pc_or_label_operand" "")
 	 (match_operand 3 "pc_or_label_operand" "")))]
   "TARGET_MIPS16"