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| -rw-r--r-- | lib/Target/README.txt | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/lib/Target/README.txt b/lib/Target/README.txt index e6178894af..b331acf032 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -524,3 +524,24 @@ Investigate lowering of sparse switch statements into perfect hash tables: 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. + +//===---------------------------------------------------------------------===// |