diff options
Diffstat (limited to 'contrib/llvm/lib/Target/ARM/README.txt')
| -rw-r--r-- | contrib/llvm/lib/Target/ARM/README.txt | 42 |
1 files changed, 21 insertions, 21 deletions
diff --git a/contrib/llvm/lib/Target/ARM/README.txt b/contrib/llvm/lib/Target/ARM/README.txt index 0cb8ff0..9fc3fb9 100644 --- a/contrib/llvm/lib/Target/ARM/README.txt +++ b/contrib/llvm/lib/Target/ARM/README.txt @@ -611,27 +611,6 @@ constant which was already loaded). Not sure what's necessary to do that. //===---------------------------------------------------------------------===// -Given the following on ARMv7: -int test1(int A, int B) { - return (A&-8388481)|(B&8388480); -} - -We currently generate: - bfc r0, #7, #16 - movw r2, #:lower16:8388480 - movt r2, #:upper16:8388480 - and r1, r1, r2 - orr r0, r1, r0 - bx lr - -The following is much shorter: - lsr r1, r1, #7 - bfi r0, r1, #7, #16 - bx lr - - -//===---------------------------------------------------------------------===// - The code generated for bswap on armv4/5 (CPUs without rev) is less than ideal: int a(int x) { return __builtin_bswap32(x); } @@ -657,3 +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. + +//===---------------------------------------------------------------------===// + |
