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(simplify_relational_operation): Don't simplify A-B for 

compare of A and B when the compare is unsigned.

From-SVN: r9296
This commit is contained in:
Jim Wilson 1995-04-02 14:34:42 -07:00
parent e3124505ec
commit c27b5c621a
1 changed files with 5 additions and 9 deletions
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14
gcc/cse.c
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@ -4378,20 +4378,16 @@ simplify_relational_operation (code, mode, op0, op1)
a register or a CONST_INT, this can't help; testing for these cases will
prevent infinite recursion here and speed things up.
If CODE is an unsigned comparison, we can only do this if A - B is a
constant integer, and then we have to compare that integer with zero as a
signed comparison. Note that this will give the incorrect result from
comparisons that overflow. Since these are undefined, this is probably
OK. If it causes a problem, we can check for A or B being an address
(fp + const or SYMBOL_REF) and only do it in that case. */
If CODE is an unsigned comparison, then we can never do this optimization,
because it gives an incorrect result if the subtraction wraps around zero.
ANSI C defines unsigned operations such that they never overflow, and
thus such cases can not be ignored. */
if (INTEGRAL_MODE_P (mode) && op1 != const0_rtx
&& ! ((GET_CODE (op0) == REG || GET_CODE (op0) == CONST_INT)
&& (GET_CODE (op1) == REG || GET_CODE (op1) == CONST_INT))
&& 0 != (tem = simplify_binary_operation (MINUS, mode, op0, op1))
&& (GET_CODE (tem) == CONST_INT
|| (code != GTU && code != GEU &&
code != LTU && code != LEU)))
&& code != GTU && code != GEU && code != LTU && code != LEU)
return simplify_relational_operation (signed_condition (code),
mode, tem, const0_rtx);