Do not simplify "(and (reg) (const bit)" to if_then_else.

combine_simplify_rtx() tries to replace rtx expressions with just two
possible values with an experession that uses if_then_else:

  (if_then_else (condition) (value1) (value2))

If the original expression is e.g.

  (and (reg) (const_int 2))

where the constant is the mask for a single bit, the replacement results
in a more complex expression than before:

  (if_then_else (ne (zero_extract (reg) (1) (31))) (2) (0))

Similar replacements are done for

  (signextend (and ...))
  (zeroextend (and ...))

Suppress the replacement this special case in if_then_else_cond().

gcc/ChangeLog:

2016-12-02  Dominik Vogt  <vogt@linux.vnet.ibm.com>

	* combine.c (combine_simplify_rtx):  Suppress replacement of
	"(and (reg) (const_int bit))" with "if_then_else".

From-SVN: r243162

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index e357932cc188aed2abe7168c00f53055e58200b6..a3fcd8b6d0b0c7b1cff9994063ab0ef72a7e6120 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2016-12-02  Dominik Vogt  <vogt@linux.vnet.ibm.com>
+
+       * combine.c (combine_simplify_rtx):  Suppress replacement of
+       "(and (reg) (const_int bit))" with "if_then_else".
+
 2016-12-02  Dominik Vogt  <vogt@linux.vnet.ibm.com>
 
        PR target/77822

diff --git a/gcc/combine.c b/gcc/combine.c
index b4294532296d477faa3a21ccc60d120cb7450568..7ba634af532a6f5ec210b71a0bd4adc890bf044e 100644 (file)
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -5602,6 +5602,18 @@ combine_simplify_rtx (rtx x, machine_mode op0_mode, int in_dest,
                     && OBJECT_P (SUBREG_REG (XEXP (x, 0)))))))
     {
       rtx cond, true_rtx, false_rtx;
+      unsigned HOST_WIDE_INT nz;
+
+      /* If the operation is an AND wrapped in a SIGN_EXTEND or ZERO_EXTEND with
+        either operand being just a constant single bit value, do nothing since
+        IF_THEN_ELSE is likely to increase the expression's complexity.  */
+      if (HWI_COMPUTABLE_MODE_P (mode)
+         && pow2p_hwi (nz = nonzero_bits (x, mode))
+         && ! ((code == SIGN_EXTEND || code == ZERO_EXTEND)
+               && GET_CODE (XEXP (x, 0)) == AND
+               && CONST_INT_P (XEXP (XEXP (x, 0), 0))
+               && UINTVAL (XEXP (XEXP (x, 0), 0)) == nz))
+             return x;
 
       cond = if_then_else_cond (x, &true_rtx, &false_rtx);
       if (cond != 0