[15/29,arm] Improve handling of DImode comparisions against constants.
diff mbox series

Message ID 20191018194900.34795-16-Richard.Earnshaw@arm.com
State New
Headers show
Series
  • Rewrite DImode arithmetic support
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Commit Message

Richard Earnshaw (lists) Oct. 18, 2019, 7:48 p.m. UTC
In almost all cases it is better to handle inequality handling against constants
by transforming comparisons of the form (reg <GE/LT/GEU/LTU> const) into
(reg <GT/LE/GTU/LEU> (const+1)).  However, there are many cases that we could
handle but currently failed to do so because we forced the constant into a
register too early in the pattern expansion.  To permit this to be done we need
to defer forcing the constant into a register until after we've had the chance
to do the transform - in some cases that may even mean that we no-longer need
to force the constant into a register at all.  For example, on Arm, the case:

_Bool f8 (unsigned long long a) { return a > 0xffffffff; }

previously compiled to

        mov     r3, #0
        cmp     r1, r3
        mvn     r2, #0
        cmpeq   r0, r2
        movhi   r0, #1
        movls   r0, #0
        bx      lr

But now compiles to

        cmp     r1, #1
        cmpeq   r0, #0
        movcs   r0, #1
        movcc   r0, #0
        bx      lr

Which although not yet completely optimal, is certainly better than
previously.

	* config/arm/arm.md (cbranchdi4): Accept reg_or_int_operand for
	operand 2.
	(cstoredi4): Similarly, but for operand 3.
	* config/arm/arm.c (arm_canoncialize_comparison): Allow canonicalization
	of unsigned compares with a constant on Arm.  Prefer using const+1 and
	adjusting the comparison over swapping the operands whenever the
	original constant was not valid.
	(arm_gen_dicompare_reg): If Y is not a valid operand, force it to a
	register here.
	(arm_validize_comparison): Do not force invalid DImode operands to
	registers here.
---
 gcc/config/arm/arm.c  | 37 +++++++++++++++++++++++--------------
 gcc/config/arm/arm.md |  4 ++--
 2 files changed, 25 insertions(+), 16 deletions(-)

Patch
diff mbox series

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 64367b42332..ddfe4335169 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -5372,15 +5372,16 @@  arm_canonicalize_comparison (int *code, rtx *op0, rtx *op1,
 
   maxval = (HOST_WIDE_INT_1U << (GET_MODE_BITSIZE (mode) - 1)) - 1;
 
-  /* For DImode, we have GE/LT/GEU/LTU comparisons.  In ARM mode
-     we can also use cmp/cmpeq for GTU/LEU.  GT/LE must be either
-     reversed or (for constant OP1) adjusted to GE/LT.  Similarly
-     for GTU/LEU in Thumb mode.  */
+  /* For DImode, we have GE/LT/GEU/LTU comparisons (with cmp/sbc).  In
+     ARM mode we can also use cmp/cmpeq for GTU/LEU.  GT/LE must be
+     either reversed or (for constant OP1) adjusted to GE/LT.
+     Similarly for GTU/LEU in Thumb mode.  */
   if (mode == DImode)
     {
 
       if (*code == GT || *code == LE
-	  || (!TARGET_ARM && (*code == GTU || *code == LEU)))
+	  || ((!TARGET_ARM || CONST_INT_P (*op1))
+	      && (*code == GTU || *code == LEU)))
 	{
 	  /* Missing comparison.  First try to use an available
 	     comparison.  */
@@ -5392,23 +5393,27 @@  arm_canonicalize_comparison (int *code, rtx *op0, rtx *op1,
 		case GT:
 		case LE:
 		  if (i != maxval
-		      && arm_const_double_by_immediates (GEN_INT (i + 1)))
+		      && (!arm_const_double_by_immediates (*op1)
+			  || arm_const_double_by_immediates (GEN_INT (i + 1))))
 		    {
 		      *op1 = GEN_INT (i + 1);
 		      *code = *code == GT ? GE : LT;
 		      return;
 		    }
 		  break;
+
 		case GTU:
 		case LEU:
 		  if (i != ~((unsigned HOST_WIDE_INT) 0)
-		      && arm_const_double_by_immediates (GEN_INT (i + 1)))
+		      && (!arm_const_double_by_immediates (*op1)
+			  || arm_const_double_by_immediates (GEN_INT (i + 1))))
 		    {
 		      *op1 = GEN_INT (i + 1);
 		      *code = *code == GTU ? GEU : LTU;
 		      return;
 		    }
 		  break;
+
 		default:
 		  gcc_unreachable ();
 		}
@@ -15436,7 +15441,7 @@  arm_gen_dicompare_reg (rtx_code code, rtx x, rtx y, rtx scratch)
 		scratch = gen_reg_rtx (SImode);
 	      if (ylo == const0_rtx)
 		{
-		  yhi = GEN_INT (-INTVAL(yhi));
+		  yhi = gen_int_mode (-INTVAL (yhi), SImode);
 		  if (!arm_add_operand (yhi, SImode))
 		    yhi = force_reg (SImode, yhi);
 		  emit_insn (gen_addsi3 (scratch, xhi, yhi));
@@ -15445,7 +15450,7 @@  arm_gen_dicompare_reg (rtx_code code, rtx x, rtx y, rtx scratch)
 	      else
 		{
 		  gcc_assert (yhi == const0_rtx);
-		  ylo = GEN_INT (-INTVAL(ylo));
+		  ylo = gen_int_mode (-INTVAL (ylo), SImode);
 		  if (!arm_add_operand (ylo, SImode))
 		    ylo = force_reg (SImode, ylo);
 		  emit_insn (gen_addsi3 (scratch, xlo, ylo));
@@ -15458,6 +15463,8 @@  arm_gen_dicompare_reg (rtx_code code, rtx x, rtx y, rtx scratch)
 	    x = gen_rtx_IOR (SImode, gen_lowpart (SImode, x),
 			     gen_highpart (SImode, x));
 	}
+      else if (!cmpdi_operand (y, mode))
+	y = force_reg (DImode, y);
 
       /* A scratch register is required.  */
       if (reload_completed)
@@ -15470,7 +15477,12 @@  arm_gen_dicompare_reg (rtx_code code, rtx x, rtx y, rtx scratch)
       emit_insn (gen_rtx_PARALLEL (VOIDmode, gen_rtvec (2, set, clobber)));
     }
   else
-    emit_set_insn (cc_reg, gen_rtx_COMPARE (mode, x, y));
+    {
+      if (!cmpdi_operand (y, mode))
+	y = force_reg (DImode, y);
+
+      emit_set_insn (cc_reg, gen_rtx_COMPARE (mode, x, y));
+    }
 
   return cc_reg;
 }
@@ -30479,10 +30491,7 @@  arm_validize_comparison (rtx *comparison, rtx * op1, rtx * op2)
       return true;
 
     case E_DImode:
-      if (!cmpdi_operand (*op1, mode))
-	*op1 = force_reg (mode, *op1);
-      if (!cmpdi_operand (*op2, mode))
-	*op2 = force_reg (mode, *op2);
+      /* gen_compare_reg() will sort out any invalid operands.  */
       return true;
 
     case E_HFmode:
diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md
index a6b0c196c58..9d8b137651f 100644
--- a/gcc/config/arm/arm.md
+++ b/gcc/config/arm/arm.md
@@ -6397,7 +6397,7 @@  (define_expand "cbranchdi4"
   [(set (pc) (if_then_else
 	      (match_operator 0 "expandable_comparison_operator"
 	       [(match_operand:DI 1 "s_register_operand")
-	        (match_operand:DI 2 "cmpdi_operand")])
+	        (match_operand:DI 2 "reg_or_int_operand")])
 	      (label_ref (match_operand 3 "" ""))
 	      (pc)))]
   "TARGET_32BIT"
@@ -6862,7 +6862,7 @@  (define_expand "cstoredi4"
   [(set (match_operand:SI 0 "s_register_operand")
 	(match_operator:SI 1 "expandable_comparison_operator"
 	 [(match_operand:DI 2 "s_register_operand")
-	  (match_operand:DI 3 "cmpdi_operand")]))]
+	  (match_operand:DI 3 "reg_or_int_operand")]))]
   "TARGET_32BIT"
   "{
      if (!arm_validize_comparison (&operands[1],