[gcc r17-2595] rs6000: Add %W print modifier

https://gcc.gnu.org/g:2ef1fe741998203a107fa81221ab6ce0428ebadc

commit r17-2595-g2ef1fe741998203a107fa81221ab6ce0428ebadc
Author: Jeevitha <[email protected]>
Date:   Tue Jul 21 10:27:29 2026 -0500

    rs6000: Add %W print modifier
    
    Add a new %W print modifier to print_operand that prints the VSX
    register number plus two.
    
    Some future Power instruction patterns require printing two VSX
    registers corresponding to a __vector_pair operand. The existing
    %x print modifier emits the first VSX register using VSX register
    numbering. Add a new %W print modifier to emit the second VSX
    register of the pair.
    
    2025-07-16  Jeevitha Palanisamy  <[email protected]>
                Kishan Parmar  <[email protected]>
    
    gcc/
            * config/rs6000/rs6000.cc (print_operand): Add the `%W`
            print modifier to print the VSX register number plus two.

Diff:
---
 gcc/config/rs6000/rs6000.cc | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index 7743c9cdc4a1..3a7327a68c63 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -14516,6 +14516,30 @@ print_operand (FILE *file, rtx x, int code)
 	print_operand (file, x, 0);
       return;
 
+    case 'W':
+      /* Like '%x', but prints the VSX register number +2.
+	  TODO: Validate %W operands (e.g. reject V30/V31 to avoid referencing
+	  invalid registers). Ensure GET_MODE_SIZE (GET_MODE (x)) >= 64
+	  before using %W.  */
+      if (!REG_P (x) || !VSX_REGNO_P (REGNO (x)))
+	output_operand_lossage ("invalid %%W value");
+      else
+	{
+	  int reg = REGNO (x);
+	  int vsx_reg = (FP_REGNO_P (reg)
+			 ? reg - 32
+			 : reg - FIRST_ALTIVEC_REGNO + 32);
+	  vsx_reg += 2;
+
+#ifdef TARGET_REGNAMES
+	  if (TARGET_REGNAMES)
+	    fprintf (file, "%%vs%d", vsx_reg);
+	  else
+#endif
+	    fprintf (file, "%d", vsx_reg);
+	}
+      return;
+
     case 'x':
       /* X is a FPR or Altivec register used in a VSX context.  */
       if (!REG_P (x) || !VSX_REGNO_P (REGNO (x)))