re PR rtl-optimization/82192 (gcc produces incorrect code with -O2 and bit-field)

	PR rtl-optimization/82192
	* combine.c (make_extraction): Don't look through non-paradoxical
	SUBREGs or TRUNCATE if pos + len is or might be bigger than
	inner's mode.

	* gcc.c-torture/execute/pr82192.c: New test.

From-SVN: r252824

gcc/ChangeLog

+2017-09-15  Jakub Jelinek  <jakub@redhat.com>
+
+	PR rtl-optimization/82192
+	* combine.c (make_extraction): Don't look through non-paradoxical
+	SUBREGs or TRUNCATE if pos + len is or might be bigger than
+	inner's mode.
+
 2017-09-15  Richard Sandiford  <richard.sandiford@linaro.org>
 	    Alan Hayward  <alan.hayward@arm.com>
 	    David Sherwood  <david.sherwood@arm.com>

gcc/combine.c

@@ -7442,7 +7442,14 @@ make_extraction (machine_mode mode, rtx inner, HOST_WIDE_INT pos,
   if (pos_rtx && CONST_INT_P (pos_rtx))
     pos = INTVAL (pos_rtx), pos_rtx = 0;
 
-  if (GET_CODE (inner) == SUBREG && subreg_lowpart_p (inner))
+  if (GET_CODE (inner) == SUBREG
+      && subreg_lowpart_p (inner)
+      && (paradoxical_subreg_p (inner)
+	  /* If trying or potentionally trying to extract
+	     bits outside of is_mode, don't look through
+	     non-paradoxical SUBREGs.  See PR82192.  */
+	  || (pos_rtx == NULL_RTX
+	      && pos + len <= GET_MODE_PRECISION (is_mode))))
     {
       /* If going from (subreg:SI (mem:QI ...)) to (mem:QI ...),
 	 consider just the QI as the memory to extract from.
@@ -7468,7 +7475,12 @@ make_extraction (machine_mode mode, rtx inner, HOST_WIDE_INT pos,
       if (new_rtx != 0)
 	return gen_rtx_ASHIFT (mode, new_rtx, XEXP (inner, 1));
     }
-  else if (GET_CODE (inner) == TRUNCATE)
+  else if (GET_CODE (inner) == TRUNCATE
+	   /* If trying or potentionally trying to extract
+	      bits outside of is_mode, don't look through
+	      TRUNCATE.  See PR82192.  */
+	   && pos_rtx == NULL_RTX
+	   && pos + len <= GET_MODE_PRECISION (is_mode))
     inner = XEXP (inner, 0);
 
   inner_mode = GET_MODE (inner);

gcc/testsuite/ChangeLog

+2017-09-15  Jakub Jelinek  <jakub@redhat.com>
+
+	PR rtl-optimization/82192
+	* gcc.c-torture/execute/pr82192.c: New test.
+
 2017-09-15  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/82217

gcc/testsuite/gcc.c-torture/execute/pr82192.c

+/* PR rtl-optimization/82192 */
+
+unsigned long long int a = 0x95dd3d896f7422e2ULL;
+struct S { unsigned int m : 13; } b;
+
+__attribute__((noinline, noclone)) void
+foo (void)
+{
+  b.m = ((unsigned) a) >> (0x644eee9667723bf7LL
+			   | a & ~0xdee27af8U) - 0x644eee9667763bd8LL;
+}
+
+int
+main ()
+{
+  if (__INT_MAX__ != 0x7fffffffULL)
+    return 0;
+  foo ();
+  if (b.m != 0)
+    __builtin_abort ();
+  return 0;
+}