OpenE2K/gcc
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

(operand_equal_p): Make it clear that this function tests for indistinguishable values, not for equality as computed by `=='...

Browse Source 
(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
This commit is contained in:
Richard Stallman 1992-08-12 07:43:50 +00:00
parent e92b33f508
commit 6a1746af42
1 changed files with 12 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
gcc/fold-const.c
View File

@ -1567,8 +1567,13 @@ swap_tree_comparison (code)
} }
} }
/* Return nonzero if two operands are necessarily equal. /* Return nonzero if two operands are necessarily equal.
If ONLY_CONST is non-zero, only return non-zero for constants. */ 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 int
operand_equal_p (arg0, arg1, only_const) 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)) && TREE_INT_CST_HIGH (arg0) == TREE_INT_CST_HIGH (arg1))
return 1; return 1;
/* Detect when real constants are equal. /* Detect when real constants are equal. */
But reject weird values because we can't be sure what to do with them. */
if (TREE_CODE (arg0) == TREE_CODE (arg1) if (TREE_CODE (arg0) == TREE_CODE (arg1)
&& TREE_CODE (arg0) == REAL_CST && TREE_CODE (arg0) == REAL_CST)
&& !bcmp (&TREE_REAL_CST (arg0), &TREE_REAL_CST (arg1), return !bcmp (&TREE_REAL_CST (arg0), &TREE_REAL_CST (arg1),
sizeof (REAL_VALUE_TYPE)) 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;
if (only_const) if (only_const)
return 0; return 0;
@ -3316,7 +3314,7 @@ fold (expr)
/* Fold &x - &x. This can happen from &x.foo - &x. /* Fold &x - &x. This can happen from &x.foo - &x.
This is unsafe for certain floats even in non-IEEE formats. This is unsafe for certain floats even in non-IEEE formats.
In IEEE, it is unsafe because it does wrong for NaNs. 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. */ is volatile. */
if (operand_equal_p (arg0, arg1, if (operand_equal_p (arg0, arg1,