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Add a note about an IRgen optimization opportunity. 

llvm-svn: 65376
This commit is contained in:
Daniel Dunbar 2009-02-24 06:34:04 +00:00
parent 0fb12efbc1
commit 36ae309434
1 changed files with 7 additions and 1 deletions
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8
clang/lib/CodeGen/README.txt
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@ -28,6 +28,12 @@ In theory, the same optimization could be a win for block local
variables as long as the declaration dominates all statements in the
block.
NOTE: The main case we care about this for is for -O0 -g compile time
performance, and in that scenario we will need to emit the alloca
anyway currently to emit proper debug info. So this is blocked by
being able to emit debug information which refers to an LLVM
temporary, not an alloca.
//===---------------------------------------------------------------------===//
We should try and avoid generating basic blocks which only contain
@ -36,7 +42,7 @@ instruction overhead), all the way down through code generation and
assembly time.
On 176.gcc:expr.ll, it looks like over 12% of basic blocks are just
direct branches.
direct branches!
//===---------------------------------------------------------------------===//