re PR rtl-optimization/53352 (Incorrect CSE optimization on RTL expressions with…

re PR rtl-optimization/53352 (Incorrect CSE optimization on RTL expressions with a paradoxical subreg)

gcc/
2012-05-15  Meador Inge  <meadori@codesourcery.com>

	PR rtl-optimization/53352
	* cse.c (equiv_constant): Ignore paradoxical subregs.

gcc/testsuite/
2012-05-15  Meador Inge  <meadori@codesourcery.com>

	PR rtl-optimization/53352
	* gcc.dg/pr53352.c: New test.

From-SVN: r187648

gcc/ChangeLog

+2012-05-18  Meador Inge  <meadori@codesourcery.com>
+
+	PR rtl-optimization/53352
+	* cse.c (equiv_constant): Ignore paradoxical subregs.
+
 2012-05-17  Steven Bosscher  <steven@gcc.gnu.org>
 
 	PR rtl-optimization/53125

gcc/cse.c

@@ -3786,8 +3786,12 @@ equiv_constant (rtx x)
 	    }
 	}
 
-      /* Otherwise see if we already have a constant for the inner REG.  */
+      /* Otherwise see if we already have a constant for the inner REG,
+	 and if that is enough to calculate an equivalent constant for
+	 the subreg.  Note that the upper bits of paradoxical subregs
+	 are undefined, so they cannot be said to equal anything.  */
       if (REG_P (SUBREG_REG (x))
+	  && GET_MODE_SIZE (mode) <= GET_MODE_SIZE (imode)
 	  && (new_rtx = equiv_constant (SUBREG_REG (x))) != 0)
         return simplify_subreg (mode, new_rtx, imode, SUBREG_BYTE (x));
 

gcc/testsuite/ChangeLog

+2012-05-18  Meador Inge  <meadori@codesourcery.com>
+
+	PR rtl-optimization/53352
+	* gcc.dg/pr53352.c: New test.
+
 2012-05-17  David S. Miller  <davem@davemloft.net>
 
 	* gfortran.dg/bessel_7.f90: Bump allowed precision to avoid

gcc/testsuite/gcc.dg/pr53352.c

+/* { dg-do run } */
+/* { dg-options "-O1" } */
+
+#include <stdlib.h>
+
+typedef union
+{
+  struct
+  {
+    unsigned char a;
+    unsigned char b;
+    unsigned char c;
+    unsigned char d;
+  } parts;
+  unsigned long whole;
+} T;
+
+T *g_t;
+
+void bar (unsigned long x)
+{
+  if (x != 0)
+    abort ();
+}
+
+int main ()
+{
+  T one;
+  T two;
+  T tmp1, tmp2;
+
+  one.whole = 0xFFE0E0E0UL;
+  two.whole = 0xFF000000UL;
+  tmp1.parts = two.parts;
+  tmp2.parts = one.parts;
+  tmp2.parts.c = tmp1.parts.c;
+  one.parts = tmp2.parts;
+
+  g_t = &one;
+  bar (0);
+}