re PR middle-end/18041 (OR of two single-bit bitfields is inefficient)

2018-11-06  Richard Biener  <rguenther@suse.de>

	PR middle-end/18041
	* simplify-rtx.c (simplify_binary_operation_1): Add pattern
	matching bitfield insertion.

	* gcc.target/i386/pr18041-1.c: New testcase.
	* gcc.target/i386/pr18041-2.c: Likewise.

From-SVN: r265829

gcc/ChangeLog

+2018-11-06  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/18041
+	* simplify-rtx.c (simplify_binary_operation_1): Add pattern
+	matching bitfield insertion.
+
 2018-11-06  Alexandre Oliva <aoliva@redhat.com>
 
 	* auto-inc-dec.c: Include valtrack.h.  Improve comments.

gcc/simplify-rtx.c

@@ -2857,6 +2857,38 @@ simplify_binary_operation_1 (enum rtx_code code, machine_mode mode,
 					XEXP (op0, 1));
         }
 
+      /* The following happens with bitfield merging.
+         (X & C) | ((X | Y) & ~C) -> X | (Y & ~C) */
+      if (GET_CODE (op0) == AND
+	  && GET_CODE (op1) == AND
+	  && CONST_INT_P (XEXP (op0, 1))
+	  && CONST_INT_P (XEXP (op1, 1))
+	  && (INTVAL (XEXP (op0, 1))
+	      == ~INTVAL (XEXP (op1, 1))))
+	{
+	  /* The IOR may be on both sides.  */
+	  rtx top0 = NULL_RTX, top1 = NULL_RTX;
+	  if (GET_CODE (XEXP (op1, 0)) == IOR)
+	    top0 = op0, top1 = op1;
+	  else if (GET_CODE (XEXP (op0, 0)) == IOR)
+	    top0 = op1, top1 = op0;
+	  if (top0 && top1)
+	    {
+	      /* X may be on either side of the inner IOR.  */
+	      rtx tem = NULL_RTX;
+	      if (rtx_equal_p (XEXP (top0, 0),
+			       XEXP (XEXP (top1, 0), 0)))
+		tem = XEXP (XEXP (top1, 0), 1);
+	      else if (rtx_equal_p (XEXP (top0, 0),
+				    XEXP (XEXP (top1, 0), 1)))
+		tem = XEXP (XEXP (top1, 0), 0);
+	      if (tem)
+		return simplify_gen_binary (IOR, mode, XEXP (top0, 0),
+					    simplify_gen_binary
+					      (AND, mode, tem, XEXP (top1, 1)));
+	    }
+	}
+
       tem = simplify_byte_swapping_operation (code, mode, op0, op1);
       if (tem)
 	return tem;

gcc/testsuite/ChangeLog

+2018-11-06  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/18041
+	* gcc.target/i386/pr18041-1.c: New testcase.
+	* gcc.target/i386/pr18041-2.c: Likewise.
+
 2018-11-06 Wei Xiao <wei3.xiao@intel.com>
 
 	* gcc.target/i386/avx-1.c: Update tests for VFIXUPIMM* intrinsics.

gcc/testsuite/gcc.target/i386/pr18041-1.c

+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+struct B { unsigned bit0 : 1; unsigned bit1 : 1; };
+
+void
+foo (struct B *b)
+{
+    b->bit0 = b->bit0 | b->bit1;
+}
+
+/* { dg-final { scan-assembler-times "and" 1 } } */
+/* { dg-final { scan-assembler-times "or" 1 } } */

gcc/testsuite/gcc.target/i386/pr18041-2.c

+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+struct B { unsigned bit0 : 1; unsigned bit1 : 1; };
+
+void
+bar  (struct B *b, int x)
+{
+  b->bit0 |= x;
+}
+
+/* This fails to combine in 32bit mode but not for x32.  */
+/* { dg-final { scan-assembler-times "and" 1 { xfail { { ! x32 } && ilp32 } } } } */
+/* { dg-final { scan-assembler-times "or" 1 { xfail { { ! x32 } && ilp32 } } } } */