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A N-bit truncate is not much different than ANDing with
a N-bit mask and so some simplifications done for AND can
also be done for TRUNC. For example for code like this:
char foo(int x, int y) { return (x & 0xffff) | y; }
the mask is unneeded and the function should be equivalent to:
char foo(int x, int y) { return x | y; }
The simplification in this patch does exactly this, giving:
foo:
or.32 %r4 <- %arg1, %arg2
trunc.8 %r5 <- (32) %r4
ret.8 %r5
while previously the mask was not optimized away:
foo:
and.32 %r2 <- %arg1, $0xffff
or.32 %r4 <- %r2, %arg2
trunc.8 %r5 <- (32) %r4
ret.8 %r5
This simplification is especially important for signed bitfields
because the TRUNC+ZEXT of unsigned bitfields is simplified into
an OP_AND but this is, of course, not the case for the TRUNC+SEXT
of signed bitfields.
Do the simplification by calling simplify_mask_or(), initialy used
for OP_AND, but with the effective mask corresponding to TRUNC(x, N):
$mask(N).
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
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