Re: [patch][ARM] Fix 16-bit -> 64-bit multiply and accumulate

[Bernd Schmidt <bernds@codesourcery.com>]

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On 04/15/2011 12:54 PM, Andrew Stubbs wrote:
> Ping.

Trying to unblock this...

I think the point is that both examples:

long long foolong (long long x, short *a, short *b)
   {
       return x + (long long)*a * (long long)*b;
   }

and


  long long foolong (long long x, short *a, short *b)
  {
      return x + *a * *b;
  }

should produce the same code using the maddhidi pattern, and for that to
happen, simplify_rtx must produce a canonical form of the 16->64 bit
widening multiply. The form that already exists in arm.md looks better
so we should pick that.

I tried to fix it with the patch below, which unfortunately doesn't work
since during combine we don't see the SIGN_EXTEND operations inside the
MULT, but two shift operations instead. Maybe you can complete it from here?


Bernd

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Index: gcc/simplify-rtx.c
===================================================================
--- gcc/simplify-rtx.c	(revision 173242)
+++ gcc/simplify-rtx.c	(working copy)
@@ -1000,6 +1000,23 @@ simplify_unary_operation_1 (enum rtx_cod
 	  && GET_CODE (XEXP (XEXP (op, 0), 1)) == LABEL_REF)
 	return XEXP (op, 0);
 
+      /* Extending a widening multiplication should be canonicalized to
+	 a wider widening multiplication.  */
+      if (GET_CODE (op) == MULT
+	  && GET_CODE (XEXP (op, 0)) == SIGN_EXTEND
+	  && GET_CODE (XEXP (op, 1)) == SIGN_EXTEND)
+	{
+	  rtx op0 = XEXP (XEXP (op, 0), 0);
+	  rtx op1 = XEXP (XEXP (op, 1), 0);
+	  enum machine_mode op0_mode = GET_MODE (op0);
+	  enum machine_mode op1_mode = GET_MODE (op1);
+	  return simplify_gen_binary (MULT, mode,
+				      simplify_gen_unary (SIGN_EXTEND, mode,
+							  op0, op0_mode),
+				      simplify_gen_unary (SIGN_EXTEND, mode,
+							  op1, op1_mode));
+	}
+
       /* Check for a sign extension of a subreg of a promoted
 	 variable, where the promotion is sign-extended, and the
 	 target mode is the same as the variable's promotion.  */
@@ -1071,6 +1088,23 @@ simplify_unary_operation_1 (enum rtx_cod
 	  && GET_MODE_SIZE (mode) <= GET_MODE_SIZE (GET_MODE (XEXP (op, 0))))
 	return rtl_hooks.gen_lowpart_no_emit (mode, op);
 
+      /* Extending a widening multiplication should be canonicalized to
+	 a wider widening multiplication.  */
+      if (GET_CODE (op) == MULT
+	  && GET_CODE (XEXP (op, 0)) == ZERO_EXTEND
+	  && GET_CODE (XEXP (op, 1)) == ZERO_EXTEND)
+	{
+	  rtx op0 = XEXP (XEXP (op, 0), 0);
+	  rtx op1 = XEXP (XEXP (op, 1), 0);
+	  enum machine_mode op0_mode = GET_MODE (op0);
+	  enum machine_mode op1_mode = GET_MODE (op1);
+	  return simplify_gen_binary (MULT, mode,
+				      simplify_gen_unary (ZERO_EXTEND, mode,
+							  op0, op0_mode),
+				      simplify_gen_unary (ZERO_EXTEND, mode,
+							  op1, op1_mode));
+	}
+
       /* (zero_extend:M (zero_extend:N <X>)) is (zero_extend:M <X>).  */
       if (GET_CODE (op) == ZERO_EXTEND)
 	return simplify_gen_unary (ZERO_EXTEND, mode, XEXP (op, 0),