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| author | Anton Korobeynikov <asl@math.spbu.ru> | 2010-07-26 21:48:35 +0000 |
|---|---|---|
| committer | Anton Korobeynikov <asl@math.spbu.ru> | 2010-07-26 21:48:35 +0000 |
| commit | b61a6f2742e0823c2d6c23e34bbd141c9367c9cb (patch) | |
| tree | 2a5e49ef014b711fd92ccd5f966eeb07af745362 | |
| parent | e83f624f4469066aedf42dda32855d7dd45f9ed8 (diff) | |
| download | bcm5719-llvm-b61a6f2742e0823c2d6c23e34bbd141c9367c9cb.tar.gz bcm5719-llvm-b61a6f2742e0823c2d6c23e34bbd141c9367c9cb.zip | |
Add a note
llvm-svn: 109448
| -rw-r--r-- | llvm/lib/Target/ARM/README.txt | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/llvm/lib/Target/ARM/README.txt b/llvm/lib/Target/ARM/README.txt index ba4e5da5a05..c31f22766af 100644 --- a/llvm/lib/Target/ARM/README.txt +++ b/llvm/lib/Target/ARM/README.txt @@ -636,3 +636,24 @@ A custom Thumb version would also be a slight improvement over the generic version. //===---------------------------------------------------------------------===// + +Consider the following simple C code: + +void foo(unsigned char *a, unsigned char *b, int *c) { + if ((*a | *b) == 0) *c = 0; +} + +currently llvm-gcc generates something like this (nice branchless code I'd say): + + ldrb r0, [r0] + ldrb r1, [r1] + orr r0, r1, r0 + tst r0, #255 + moveq r0, #0 + streq r0, [r2] + bx lr + +Note that both "tst" and "moveq" are redundant. + +//===---------------------------------------------------------------------===// + |
