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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 | 25a6ab0144f5e206729cb38da654c256d1672aac (patch) | |
| tree | a6d3f6dd86b4e200d2e7462fb1194e443df4e4f3 /lib/Target/ARM/README.txt | |
| parent | 72eb3007150837e4996485457ff120e3ad1c10fa (diff) | |
| download | llvm-25a6ab0144f5e206729cb38da654c256d1672aac.tar.gz llvm-25a6ab0144f5e206729cb38da654c256d1672aac.tar.bz2 llvm-25a6ab0144f5e206729cb38da654c256d1672aac.tar.xz | |
Add a note
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@109448 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Target/ARM/README.txt')
| -rw-r--r-- | lib/Target/ARM/README.txt | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/lib/Target/ARM/README.txt b/lib/Target/ARM/README.txt index ba4e5da5a0..c31f22766a 100644 --- a/lib/Target/ARM/README.txt +++ b/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. + +//===---------------------------------------------------------------------===// + |