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| author | Bill Wendling <isanbard@gmail.com> | 2008-12-02 05:12:47 +0000 |
|---|---|---|
| committer | Bill Wendling <isanbard@gmail.com> | 2008-12-02 05:12:47 +0000 |
| commit | 3bdcda82a5e6650f6ba297e9e8bf1b511d79e4fb (patch) | |
| tree | 8f318350141d6e909228a4914fe8b404b4c2f0c9 /lib/Target/README.txt | |
| parent | a8bb13f989a68030a30181823c58aab6e9c1cc0a (diff) | |
| download | llvm-3bdcda82a5e6650f6ba297e9e8bf1b511d79e4fb.tar.gz llvm-3bdcda82a5e6650f6ba297e9e8bf1b511d79e4fb.tar.bz2 llvm-3bdcda82a5e6650f6ba297e9e8bf1b511d79e4fb.tar.xz | |
- Remove the buggy -X/C -> X/-C transform. This isn't valid when X isn't a
constant. If X is a constant, then this is folded elsewhere.
- Added a note to Target/README.txt to indicate that we'd like to implement
this when we're able.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60399 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Target/README.txt')
| -rw-r--r-- | lib/Target/README.txt | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/lib/Target/README.txt b/lib/Target/README.txt index fb6b0cd53d..3c689dbe46 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -1242,3 +1242,13 @@ Should combine to "20 * (((unsigned)x) & -2)". Currently not optimized with "clang -emit-llvm-bc | opt -std-compile-opts". //===---------------------------------------------------------------------===// + +We would like to do the following transform in the instcombiner: + + -X/C -> X/-C + +However, this isn't valid if (-X) overflows. We can implement this when we +have the concept of a "C signed subtraction" operator that which is undefined +on overflow. + +//===---------------------------------------------------------------------===// |