diff options
Diffstat (limited to 'lib')
| -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. + +//===---------------------------------------------------------------------===// + |