Displaying 3 results from an estimated 3 matches for "c7c5a56a".
2012 Apr 17
2
[LLVMdev] InstCombine adds bit masks, confuses self, others
...bh/bh 1.074 1.287 +19.9% +79mB
(Running on Sandy Bridge, x86-64)
I'll try to figure out why.
/jakob
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2012 Apr 16
0
[LLVMdev] InstCombine adds bit masks, confuses self, others
On Tue, Apr 17, 2012 at 12:23 AM, Jakob Stoklund Olesen <stoklund at 2pi.dk>wrote:
> I am not sure how best to fix this. If possible, InstCombine's
> canonicalization shouldn't hide arithmetic progressions behind bit masks.
The entire concept of cleverly converting arithmetic to bit masks seems
like the perfect domain for DAGCombine instead of InstCombine:
1) We know the
2012 Apr 16
5
[LLVMdev] InstCombine adds bit masks, confuses self, others
Look at this silly function:
$ cat small.c
unsigned f(unsigned a, unsigned *p) {
unsigned x = a/4;
p[0] = x;
p[1] = x+x;
return p[1] - 2*p[0];
}
GCC turns this into straightforward code and figures out the 0 return value:
shrl $2, %edi
movl %edi, (%rsi)
addl %edi, %edi
movl %edi, 4(%rsi)
movl $0, %eax
ret
LLVM optimizes the code:
$ clang -O -S -o- small.c -emit-llvm
define i32