[Bug rtl-optimization/82192] [5/6/7/8 Regression] gcc produces incorrect code with -O2 and bit-field

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82192

--- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So like this (untested) or somewhere else?

--- gcc/combine.c.jj    2017-09-14 10:04:56.000000000 +0200
+++ gcc/combine.c       2017-09-14 16:59:28.529783572 +0200
@@ -7444,7 +7444,14 @@ make_extraction (machine_mode mode, rtx
   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.
@@ -7470,7 +7477,12 @@ make_extraction (machine_mode mode, rtx
       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/gcc.c-torture/execute/pr82192.c.jj    2017-09-14
17:02:54.281234432 +0200
+++ gcc/testsuite/gcc.c-torture/execute/pr82192.c       2017-09-14
17:02:39.000000000 +0200
@@ -0,0 +1,22 @@
+/* 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;
+}