[PATCH] Fix folding of logb (-Inf) (PR tree-optimization/57066)

[Marek Polacek]

This is an attempt to fix PR57066, where when folding logb call,
we returned -Inf for logb(-Inf), which is not correct.

I had to adjust one testcase, because it checked for a wrong value.

What I don't know yet is what we should return for -Nan, it should be
in C9X standard, but I don't have it by hand.

Does this look sane?  So far regtested/bootstrapped on x86_64-linux.

2013-04-25  Marek Polacek  <pola...@redhat.com>

        * builtins.c (fold_builtin_logb): Return +Inf for -Inf.

        * gcc.dg/torture/builtin-logb-1.c: Adjust testcase.

--- gcc/builtins.c.mp   2013-04-25 12:52:37.463451032 +0200
+++ gcc/builtins.c      2013-04-25 14:26:33.963099851 +0200
@@ -9698,7 +9698,12 @@ fold_builtin_logb (location_t loc, tree
       case rvc_inf:
        /* If arg is Inf or NaN and we're logb, return it.  */
        if (TREE_CODE (rettype) == REAL_TYPE)
-         return fold_convert_loc (loc, rettype, arg);
+         {
+           /* For logb(-Inf) we have to return +Inf.  */
+           if (value->cl == rvc_inf && !tree_expr_nonnegative_p (arg))
+             real_inf (TREE_REAL_CST_PTR (arg));
+           return fold_convert_loc (loc, rettype, arg);
+         }
        /* Fall through... */
       case rvc_zero:
        /* Zero may set errno and/or raise an exception for logb, also
--- gcc/testsuite/gcc.dg/torture/builtin-logb-1.c.mp    2013-04-25 
13:23:18.408224450 +0200
+++ gcc/testsuite/gcc.dg/torture/builtin-logb-1.c       2013-04-25 
14:28:48.900534671 +0200
@@ -48,19 +48,19 @@ extern void link_error(int);
 /* Test if FUNCRES(FUNC(NEG FUNCARG(ARGARG))) is false.  Check the
    sign as well.  */
 #ifndef __SPU__
-#define TESTIT3(FUNC,NEG,FUNCARG,ARGARG,FUNCRES) do { \
+#define TESTIT3(FUNC,NEG,FUNCARG,ARGARG,FUNCRES,NEG2) do { \
   if (!__builtin_##FUNCRES##f(__builtin_##FUNC(NEG 
__builtin_##FUNCARG##f(ARGARG))) \
-      || CKSGN_F(__builtin_##FUNC##f(NEG __builtin_##FUNCARG##f(ARGARG)), NEG 
__builtin_##FUNCARG##f(ARGARG))) \
+      || CKSGN_F(__builtin_##FUNC##f(NEG __builtin_##FUNCARG##f(ARGARG)), NEG2 
__builtin_##FUNCARG##f(ARGARG))) \
     link_error(__LINE__); \
   if (!__builtin_##FUNCRES(__builtin_##FUNC(NEG __builtin_##FUNCARG(ARGARG))) \
-      || CKSGN(__builtin_##FUNC(NEG __builtin_##FUNCARG(ARGARG)), NEG 
__builtin_##FUNCARG(ARGARG))) \
+      || CKSGN(__builtin_##FUNC(NEG __builtin_##FUNCARG(ARGARG)), NEG2 
__builtin_##FUNCARG(ARGARG))) \
     link_error(__LINE__); \
   if (!__builtin_##FUNCRES##l(__builtin_##FUNC##l(NEG 
__builtin_##FUNCARG##l(ARGARG))) \
-      || CKSGN_L(__builtin_##FUNC##l(NEG __builtin_##FUNCARG##l(ARGARG)), NEG 
__builtin_##FUNCARG##l(ARGARG))) \
+      || CKSGN_L(__builtin_##FUNC##l(NEG __builtin_##FUNCARG##l(ARGARG)), NEG2 
__builtin_##FUNCARG##l(ARGARG))) \
     link_error(__LINE__); \
   } while (0)
 #else
-#define TESTIT3(FUNC,NEG,FUNCARG,ARGARG,FUNCRES) do { \
+#define TESTIT3(FUNC,NEG,FUNCARG,ARGARG,FUNCRES,NEG2) do { \
   /* SPU single-precision floating point format does not support Inf or Nan.  
*/ \
   if (!__builtin_##FUNCRES(__builtin_##FUNC(NEG __builtin_##FUNCARG(ARGARG))) \
       || CKSGN(__builtin_##FUNC(NEG __builtin_##FUNCARG(ARGARG)), NEG 
__builtin_##FUNCARG(ARGARG))) \
@@ -173,15 +173,15 @@ foo(void)
 
   /* Test for f(+-Inf) -> +-Inf and f(+-NaN) -> +-NaN, regardless of
      the radix.  */
-  TESTIT3 (logb, ,inf, , isinf);
-  TESTIT3 (logb, - ,inf, , isinf);
-  TESTIT3 (logb,  ,nan, "", isnan);
-  TESTIT3 (logb, - ,nan, "", isnan);
-
-  TESTIT3 (significand, ,inf, , isinf);
-  TESTIT3 (significand, - ,inf, , isinf);
-  TESTIT3 (significand,  ,nan, "", isnan);
-  TESTIT3 (significand, - ,nan, "", isnan);
+  TESTIT3 (logb, ,inf, , isinf, );
+  TESTIT3 (logb, - ,inf, , isinf, );
+  TESTIT3 (logb,  ,nan, "", isnan, );
+  TESTIT3 (logb, - ,nan, "", isnan, -);
+
+  TESTIT3 (significand, ,inf, , isinf, );
+  TESTIT3 (significand, - ,inf, , isinf, -);
+  TESTIT3 (significand,  ,nan, "", isnan, );
+  TESTIT3 (significand, - ,nan, "", isnan, -);
 }
 
 int main()

        Marek