Fix RTL simplifications of FFS, POPCOUNT and PARITY.

In 2011, the rtl.texi documentation was updated to reflect that the
modes of the RTX unary operations FFS, POPCOUNT and PARITY should
match those of their operands.  Unfortunately, some of the transformations
in simplify-rtx.cc predate this tightening of RTL semantics, and have
not (until now) been updated/fixed.  i.e. The POPCOUNT and PARITY
optimizations were "correct" when I added them back in 2007.

2023-02-27  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* simplify-rtx.cc (simplify_unary_operation_1) <case FFS>: Avoid
	generating FFS with mismatched operand and result modes, by using
	an explicit SIGN_EXTEND/ZERO_EXTEND.
	<case POPCOUNT>: Likewise, for POPCOUNT of ZERO_EXTEND.
	<case PARITY>: Likewise, for PARITY of {ZERO,SIGN}_EXTEND.

diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc
index 3955929..2c82256 100644 (file)
--- a/gcc/simplify-rtx.cc
+++ b/gcc/simplify-rtx.cc
@@ -1404,22 +1404,32 @@ simplify_context::simplify_unary_operation_1 (rtx_code code, machine_mode mode,
       break;
 
     case FFS:
-      /* (ffs (*_extend <X>)) = (ffs <X>) */
+      /* (ffs (*_extend <X>)) = (*_extend (ffs <X>)).  */
       if (GET_CODE (op) == SIGN_EXTEND
          || GET_CODE (op) == ZERO_EXTEND)
-       return simplify_gen_unary (FFS, mode, XEXP (op, 0),
-                                  GET_MODE (XEXP (op, 0)));
+       {
+         temp = simplify_gen_unary (FFS, GET_MODE (XEXP (op, 0)),
+                                    XEXP (op, 0), GET_MODE (XEXP (op, 0)));
+         return simplify_gen_unary (GET_CODE (op), mode, temp,
+                                    GET_MODE (temp));
+       }
       break;
 
     case POPCOUNT:
       switch (GET_CODE (op))
        {
        case BSWAP:
-       case ZERO_EXTEND:
-         /* (popcount (zero_extend <X>)) = (popcount <X>) */
+         /* (popcount (bswap <X>)) = (popcount <X>).  */
          return simplify_gen_unary (POPCOUNT, mode, XEXP (op, 0),
                                     GET_MODE (XEXP (op, 0)));
 
+       case ZERO_EXTEND:
+         /* (popcount (zero_extend <X>)) = (zero_extend (popcount <X>)).  */
+         temp = simplify_gen_unary (POPCOUNT, GET_MODE (XEXP (op, 0)),
+                                    XEXP (op, 0), GET_MODE (XEXP (op, 0)));
+         return simplify_gen_unary (ZERO_EXTEND, mode, temp,
+                                    GET_MODE (temp));
+
        case ROTATE:
        case ROTATERT:
          /* Rotations don't affect popcount.  */
@@ -1438,11 +1448,16 @@ simplify_context::simplify_unary_operation_1 (rtx_code code, machine_mode mode,
        {
        case NOT:
        case BSWAP:
-       case ZERO_EXTEND:
-       case SIGN_EXTEND:
          return simplify_gen_unary (PARITY, mode, XEXP (op, 0),
                                     GET_MODE (XEXP (op, 0)));
 
+       case ZERO_EXTEND:
+       case SIGN_EXTEND:
+         temp = simplify_gen_unary (PARITY, GET_MODE (XEXP (op, 0)),
+                                    XEXP (op, 0), GET_MODE (XEXP (op, 0)));
+         return simplify_gen_unary (GET_CODE (op), mode, temp,
+                                    GET_MODE (temp));
+
        case ROTATE:
        case ROTATERT:
          /* Rotations don't affect parity.  */