[gcc r14-6192] rs6000: Canonicalize copysign (x, -1) back to -abs (x) in the backend [PR112606]

[gcc r14-6192] rs6000: Canonicalize copysign (x, -1) back to -abs (x) in the backend [PR112606]

[Jakub Jelinek]

https://gcc.gnu.org/g:58d5546af901364f85588fe668559d76f09e6df9

commit r14-6192-g58d5546af901364f85588fe668559d76f09e6df9
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Dec 5 21:39:31 2023 +0100

    rs6000: Canonicalize copysign (x, -1) back to -abs (x) in the backend [PR112606]
    
    The middle-end has been changed quite recently to canonicalize
    -abs (x) to copysign (x, -1) rather than the other way around.
    While I agree with that at GIMPLE level, since it matches the GIMPLE
    goal of as few operations as possible for a canonical form (-abs (x)
    is 2 GIMPLE statements, copysign (x, -1) is just one), I must say
    I don't really like that being done on RTL as well (or at least
    not canonicalizing (COPYSIGN x, negative) back to (NEG (ABS x))),
    because on most targets most of floating point constants need to be loaded
    from memory, there are a few exceptions but -1 is often not one of them.
    
    Anyway, the following patch fixes the rs6000 regression caused by the
    change in GIMPLE canonicalization (i.e. the desirable one).  As rs6000
    clearly prefers -abs (x) form because it has a single instruction to do
    that while it also has copysign instruction, but that requires loading the
    -1 from memory, the following patch just ensures the copysign expander
    can actually see the floating point constant and in that case emits the
    -abs (x) code (or in the hypothetical case of copysign with non-negative
    constant abs (x) - but there copysign (x, 1) in GIMPLE is canonicalized
    to abs (x)), otherwise forces the operand to be the expected gpc_reg_operand
    and does what it did before.
    
    2023-12-05  Jakub Jelinek  <jakub@redhat.com>
    
            PR target/112606
            * config/rs6000/rs6000.md (copysign<mode>3): Change predicate
            of the last argument from gpc_reg_operand to any_operand.  If
            operands[2] is CONST_DOUBLE, emit abs or neg abs depending on
            its sign, otherwise if it doesn't satisfy gpc_reg_operand,
            force it to REG using copy_to_mode_reg.

Diff:
---
 gcc/config/rs6000/rs6000.md | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/gcc/config/rs6000/rs6000.md b/gcc/config/rs6000/rs6000.md
index 2a1b5ecfaee..28482e3617e 100644
--- a/gcc/config/rs6000/rs6000.md
+++ b/gcc/config/rs6000/rs6000.md
@@ -5358,7 +5358,7 @@
    (set (match_dup 4)
 	(neg:SFDF (abs:SFDF (match_dup 1))))
    (set (match_operand:SFDF 0 "gpc_reg_operand")
-        (if_then_else:SFDF (ge (match_operand:SFDF 2 "gpc_reg_operand")
+	(if_then_else:SFDF (ge (match_operand:SFDF 2 "any_operand")
 			       (match_dup 5))
 			 (match_dup 3)
 			 (match_dup 4)))]
@@ -5369,6 +5369,24 @@
        || TARGET_CMPB
        || VECTOR_UNIT_VSX_P (<MODE>mode))"
 {
+  /* Middle-end canonicalizes -fabs (x) to copysign (x, -1),
+     but PowerPC prefers -fabs (x).  */
+  if (CONST_DOUBLE_AS_FLOAT_P (operands[2]))
+    {
+      if (real_isneg (CONST_DOUBLE_REAL_VALUE (operands[2])))
+	{
+	  operands[3] = gen_reg_rtx (<MODE>mode);
+	  emit_insn (gen_abs<mode>2 (operands[3], operands[1]));
+	  emit_insn (gen_neg<mode>2 (operands[0], operands[3]));
+	}
+      else
+	emit_insn (gen_abs<mode>2 (operands[0], operands[1]));
+      DONE;
+    }
+
+  if (!gpc_reg_operand (operands[2], <MODE>mode))
+    operands[2] = copy_to_mode_reg (<MODE>mode, operands[2]);
+
   if (TARGET_CMPB || VECTOR_UNIT_VSX_P (<MODE>mode))
     {
       emit_insn (gen_copysign<mode>3_fcpsgn (operands[0], operands[1],