[PATCH] Limit some match.pd conversion folding to GIMPLE (PR c++/70336)

[Jakub Jelinek]

Hi!

As the testcase shows, the folding which previously has been done
only in tree-ssa-forwprop.c breaks some cases with explicit casts
in -Wconversion, so this patch limits that folding to GIMPLE only.
Unfortunately that breaks a few cases in builtin-isinf_sign-1.c
test at -O0, but IMNSHO expecting all the folding at -O0 is wrong,
outside of constexpr and initializers we shouldn't guarantee any
folding.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2016-04-05  Jakub Jelinek  <ja...@redhat.com>

        PR c++/70336
        * match.pd (nested int casts): Limit to GIMPLE.

        * c-c++-common/pr70336.c: New test.
        * gcc.dg/torture/builtin-isinf_sign-1.c (foo): Guard tests
        no longer optimized away at -O0 with #ifndef __OPTIMIZE__.

--- gcc/match.pd.jj     2016-03-23 19:25:56.000000000 +0100
+++ gcc/match.pd        2016-04-04 12:39:32.535498926 +0200
@@ -1554,7 +1554,8 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 
     /* A truncation to an unsigned type (a zero-extension) should be
        canonicalized as bitwise and of a mask.  */
-    (if (final_int && inter_int && inside_int
+    (if (GIMPLE /* PR70366: doing this in GENERIC breaks -Wconversion.  */
+        && final_int && inter_int && inside_int
         && final_prec == inside_prec
         && final_prec > inter_prec
         && inter_unsignedp)
--- gcc/testsuite/c-c++-common/pr70336.c.jj     2016-04-04 12:42:48.056806268 
+0200
+++ gcc/testsuite/c-c++-common/pr70336.c        2016-04-04 12:44:19.343549096 
+0200
@@ -0,0 +1,37 @@
+/* PR c++/70336 */
+/* { dg-do compile } */
+/* { dg-options "-Wconversion" } */
+
+void
+f1 (unsigned char * x, int y, int z)
+{
+  x[z / 8] |= (unsigned char) (0x80 >> y);     /* { dg-bogus "may alter its 
value" } */
+}
+
+unsigned char
+f2 (unsigned char x, int y)
+{
+  x = x | (unsigned char) (0x80 >> y);         /* { dg-bogus "may alter its 
value" } */
+  return x;
+}
+
+unsigned char
+f3 (unsigned char x, int y)
+{
+  x = x | (unsigned char) (y & 255);           /* { dg-bogus "may alter its 
value" } */
+  return x;
+}
+
+unsigned char
+f4 (unsigned char x, unsigned char y)
+{
+  x = x | (unsigned char) (y & 255);           /* { dg-bogus "may alter its 
value" } */
+  return x;
+}
+
+unsigned char
+f5 (unsigned char x, int y)
+{
+  x = (unsigned char) (y & 255);               /* { dg-bogus "may alter its 
value" } */
+  return x;
+}
--- gcc/testsuite/gcc.dg/torture/builtin-isinf_sign-1.c.jj      2008-09-05 
12:54:28.000000000 +0200
+++ gcc/testsuite/gcc.dg/torture/builtin-isinf_sign-1.c 2016-04-05 
16:13:40.649320108 +0200
@@ -24,6 +24,7 @@ foo (float f, double d, long double ld)
       != (__builtin_isinf(ld) ? (__builtin_signbitl(ld) ? -1 : 1) : 0))
     link_error (__LINE__);
 
+#ifdef __OPTIMIZE__
   /* In boolean contexts, GCC will fold the inner conditional
      expression to 1.  So isinf_sign folds to plain isinf.  */
 
@@ -33,6 +34,7 @@ foo (float f, double d, long double ld)
     link_error (__LINE__);
   if ((_Bool)__builtin_isinf_sign(ld) != (__builtin_isinf(ld) != 0))
     link_error (__LINE__);
+#endif
 
   if ((__builtin_isinf_sign(f) != 0) != (__builtin_isinf(f) != 0))
     link_error (__LINE__);

        Jakub