From 6a1746af423210c8419b7e90d0954ed28f9e8535 Mon Sep 17 00:00:00 2001 From: Richard Stallman Date: Wed, 12 Aug 1992 07:43:50 +0000 Subject: [PATCH] (operand_equal_p): Make it clear that this function tests for indistinguishable values, not for equality as computed by `=='... (operand_equal_p): Make it clear that this function tests for indistinguishable values, not for equality as computed by `=='; the distinction is important for IEEE NaNs and -0.0. From-SVN: r1807 --- gcc/fold-const.c | 26 ++++++++++++-------------- 1 file changed, 12 insertions(+), 14 deletions(-) diff --git a/gcc/fold-const.c b/gcc/fold-const.c index 6a1297097ad..a7107500f23 100644 --- a/gcc/fold-const.c +++ b/gcc/fold-const.c @@ -1567,8 +1567,13 @@ swap_tree_comparison (code) } } -/* Return nonzero if two operands are necessarily equal. - If ONLY_CONST is non-zero, only return non-zero for constants. */ +/* Return nonzero if two operands are necessarily equal. + If ONLY_CONST is non-zero, only return non-zero for constants. + This function tests whether the operands are indistinguishable; + it does not test whether they are equal using C's == operation. + The distinction is important for IEEE floating point, because + (1) -0.0 and 0.0 are distinguishable, but -0.0==0.0, and + (2) two NaNs may be indistinguishable, but NaN!=NaN. */ int operand_equal_p (arg0, arg1, only_const) @@ -1604,18 +1609,11 @@ operand_equal_p (arg0, arg1, only_const) && TREE_INT_CST_HIGH (arg0) == TREE_INT_CST_HIGH (arg1)) return 1; - /* Detect when real constants are equal. - But reject weird values because we can't be sure what to do with them. */ + /* Detect when real constants are equal. */ if (TREE_CODE (arg0) == TREE_CODE (arg1) - && TREE_CODE (arg0) == REAL_CST - && !bcmp (&TREE_REAL_CST (arg0), &TREE_REAL_CST (arg1), - sizeof (REAL_VALUE_TYPE)) - /* Some people say these are not necessary. - But they do little harm, and taking them out would be risky. - So leave them and let's not spend any more time on them--rms. */ - && !REAL_VALUE_ISINF (TREE_REAL_CST (arg0)) - && !REAL_VALUE_ISNAN (TREE_REAL_CST (arg0))) - return 1; + && TREE_CODE (arg0) == REAL_CST) + return !bcmp (&TREE_REAL_CST (arg0), &TREE_REAL_CST (arg1), + sizeof (REAL_VALUE_TYPE)); if (only_const) return 0; @@ -3316,7 +3314,7 @@ fold (expr) /* Fold &x - &x. This can happen from &x.foo - &x. This is unsafe for certain floats even in non-IEEE formats. In IEEE, it is unsafe because it does wrong for NaNs. - Also note that operand_equal_p is always false is an operand + Also note that operand_equal_p is always false if an operand is volatile. */ if (operand_equal_p (arg0, arg1, -- 2.30.2