[LLVMbugs] [Bug 20543] New: Document optimization flags

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Aug 5 04:25:36 PDT 2014


            Bug ID: 20543
           Summary: Document optimization flags
           Product: clang
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Documentation
          Assignee: unassignedclangbugs at nondot.org
          Reporter: gonzalobg88 at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

I have tried to find documentation about the optimization flags available
in the current version of clang (ToT) without much success (both in the
webpage, the manual, and google).  Google always points me to:
http://clang.llvm.org/docs/UsersManual.html but I see no information there
regarding optimization levels/flags.

I'm particularly interested in:

- which optimization flags are there and a description of what they do
(e.g. -ffast-math),

- which optimization levels are there (e.g. O2) and which flags does each
level enable,

- which potentially-useful but unstable/not supported llvm optimization options
are there (e.g. -mllvm -inline-threshold=value has a large impact on
performance [0]) and a link to the llvm docs that describe them.

I asked this in the mailing list [1] but no answers so far. Anyhow, even if
this is already documented somewhere it should be easier to find than it is

[0] http://www.reddit.com/r/cpp/comments/24663s/range_comprehensions/ch46dye
[1] http://lists.cs.uiuc.edu/pipermail/cfe-users/2014-July/000541.html

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