llvm-6502/lib/Target/Alpha/README.txt

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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Fix Ordered/Unordered FP stuff
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
improve bytezap opertunities
ulong %foo(ulong %y) {
entry:
%tmp = and ulong %y, 65535
%tmp2 = shr ulong %tmp, ubyte 3
ret ulong %tmp2
}
compiles to a 3 instruction sequence without instcombine
zapnot $16,3,$0
srl $0,3,$0
ret $31,($26),1
After instcombine you get
ulong %foo(ulong %y) {
entry:
%tmp = shr ulong %y, ubyte 3 ; <ulong> [#uses=1]
%tmp2 = and ulong %tmp, 8191 ; <ulong> [#uses=1]
ret ulong %tmp2
}
which compiles to
lda $0,8191($31)
srl $16,3,$1
and $1,$0,$0
ret $31,($26),1