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| author | Duncan Sands <baldrick@free.fr> | 2011-01-14 00:37:45 +0000 |
|---|---|---|
| committer | Duncan Sands <baldrick@free.fr> | 2011-01-14 00:37:45 +0000 |
| commit | c43cee3fbb3098f0647e50dd2c13bc55b027a228 (patch) | |
| tree | 1e584c101d4d96ef46988fd14f156b4e74b21ec4 /lib/VMCore | |
| parent | 68a659d423b56e3cafcc3751b33e2472bb191048 (diff) | |
| download | external_llvm-c43cee3fbb3098f0647e50dd2c13bc55b027a228.zip external_llvm-c43cee3fbb3098f0647e50dd2c13bc55b027a228.tar.gz external_llvm-c43cee3fbb3098f0647e50dd2c13bc55b027a228.tar.bz2 | |
Move some shift transforms out of instcombine and into InstructionSimplify.
While there, I noticed that the transform "undef >>a X -> undef" was wrong.
For example if X is 2 then the top two bits must be equal, so the result can
not be anything. I fixed this in the constant folder as well. Also, I made
the transform for "X << undef" stronger: it now folds to undef always, even
though X might be zero. This is in accordance with the LangRef, but I must
admit that it is fairly aggressive. Also, I added "i32 X << 32 -> undef"
following the LangRef and the constant folder, likewise fairly aggressive.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123417 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/VMCore')
| -rw-r--r-- | lib/VMCore/ConstantFold.cpp | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/lib/VMCore/ConstantFold.cpp b/lib/VMCore/ConstantFold.cpp index 2767656..3dc7847 100644 --- a/lib/VMCore/ConstantFold.cpp +++ b/lib/VMCore/ConstantFold.cpp @@ -977,8 +977,8 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, return Constant::getNullValue(C1->getType()); // X lshr undef -> 0 // undef lshr X -> 0 case Instruction::AShr: - if (!isa<UndefValue>(C2)) - return C1; // undef ashr X --> undef + if (!isa<UndefValue>(C2)) // undef ashr X --> all ones + return Constant::getAllOnesValue(C1->getType()); else if (isa<UndefValue>(C1)) return C1; // undef ashr undef -> undef else |