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llvm-svn: 45766
This commit is contained in:
Chris Lattner 2008-01-09 00:17:57 +00:00
parent 66a26044f8
commit 45e5032b1d
1 changed files with 21 additions and 0 deletions
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21
llvm/lib/Target/README.txt
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@ -524,3 +524,24 @@ Investigate lowering of sparse switch statements into perfect hash tables:
http://burtleburtle.net/bob/hash/perfect.html http://burtleburtle.net/bob/hash/perfect.html
//===---------------------------------------------------------------------===// //===---------------------------------------------------------------------===//
We should turn things like "load+fabs+store" and "load+fneg+store" into the
corresponding integer operations. On a yonah, this loop:
double a[256];
for (b = 0; b < 10000000; b++)
for (i = 0; i < 256; i++)
a[i] = -a[i];
is twice as slow as this loop:
long long a[256];
for (b = 0; b < 10000000; b++)
for (i = 0; i < 256; i++)
a[i] ^= (1ULL << 63);
and I suspect other processors are similar. On X86 in particular this is a
big win because doing this with integers allows the use of read/modify/write
instructions.
//===---------------------------------------------------------------------===//