[patch] Lno branch merge part 8 -- canonical induction variable creation
Joseph S. Myers
Fri Aug 27 16:28:00 GMT 2004
On Fri, 27 Aug 2004, Zdenek Dvorak wrote:
> here is the patch that implements the proposal. Some remarks:
How do you ensure that expressions with the same operands but different
overflow flags don't get treated as the same? I don't see anything in
operand_equal_p to do so.
The problem case is that some transformation leaves a program with both
modulo and undefined operations with the same operands; then the version
with modulo wrapping is found to be redundant and its value is replaced by
that of the version with undefined wrapping; then that version is further
transformed in a way unsafe for the use expecting modulo wrapping.
Although such replacements are valid in one direction only (replacing the
value with undefined overflow handling with the value with modulo overflow
handling), simply disallowing them is probably easier.
Joseph S. Myers http://www.srcf.ucam.org/~jsm28/gcc/
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