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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31976 91177308-0d34-0410-b5e6-96231b3b80d8
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Evan Cheng 2006-11-28 19:59:25 +00:00
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lib/Target/X86/README.txt
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@ -730,3 +730,23 @@ to avoid the copy. In fact, the existing two-address stuff would do this
except that mul isn't a commutative 2-addr instruction. I guess this has
to be done at isel time based on the #uses to mul?
//===---------------------------------------------------------------------===//
Make sure the instruction which starts a loop does not cross a cacheline
boundary. This requires knowning the exact length of each machine instruction.
That is somewhat complicated, but doable. Example 256.bzip2:
In the new trace, the hot loop has an instruction which crosses a cacheline
boundary. In addition to potential cache misses, this can't help decoding as I
imagine there has to be some kind of complicated decoder reset and realignment
to grab the bytes from the next cacheline.
532 532 0x3cfc movb (1809(%esp, %esi), %bl <<<--- spans 2 64 byte lines
942 942 0x3d03 movl %dh, (1809(%esp, %esi)
937 937 0x3d0a incl %esi
3 3 0x3d0b cmpb %bl, %dl
27 27 0x3d0d jnz 0x000062db <main+11707>
//===---------------------------------------------------------------------===//
In c99 mode, the preprocessor doesn't like assembly comments like #TRUNCATE.