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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
This commit is contained in:
Dominik Vogt 2016-12-02 08:32:40 +00:00 committed by Andreas Krebbel
parent bba13c0c43
commit 32ff7e39c1
2 changed files with 17 additions and 0 deletions
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5
gcc/ChangeLog
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@ -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

12
gcc/combine.c
View File

@ -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