diff options
Diffstat (limited to 'include/llvm/Transforms')
| -rw-r--r-- | include/llvm/Transforms/Utils/SSAUpdater.h | 30 |
1 files changed, 27 insertions, 3 deletions
diff --git a/include/llvm/Transforms/Utils/SSAUpdater.h b/include/llvm/Transforms/Utils/SSAUpdater.h index 2897af9..8af50e3 100644 --- a/include/llvm/Transforms/Utils/SSAUpdater.h +++ b/include/llvm/Transforms/Utils/SSAUpdater.h @@ -48,16 +48,40 @@ public: /// updates. ProtoValue is the value used to name PHI nodes. void Initialize(Value *ProtoValue); - /// AddAvailableValue - Indicate that a rewritten value is available in the - /// specified block with the specified value. + /// AddAvailableValue - Indicate that a rewritten value is available at the + /// end of the specified block with the specified value. void AddAvailableValue(BasicBlock *BB, Value *V); /// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is /// live at the end of the specified block. Value *GetValueAtEndOfBlock(BasicBlock *BB); + /// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that + /// is live in the middle of the specified block. + /// + /// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one + /// important case: if there is a definition of the rewritten value after the + /// 'use' in BB. Consider code like this: + /// + /// X1 = ... + /// SomeBB: + /// use(X) + /// X2 = ... + /// br Cond, SomeBB, OutBB + /// + /// In this case, there are two values (X1 and X2) added to the AvailableVals + /// set by the client of the rewriter, and those values are both live out of + /// their respective blocks. However, the use of X happens in the *middle* of + /// a block. Because of this, we need to insert a new PHI node in SomeBB to + /// merge the appropriate values, and this value isn't live out of the block. + /// + Value *GetValueInMiddleOfBlock(BasicBlock *BB); + /// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes, - /// which use their value in the corresponding predecessor. + /// which use their value in the corresponding predecessor. Note that this + /// will not work if the use is supposed to be rewritten to a value defined in + /// the same block as the use, but above it. Any 'AddAvailableValue's added + /// for the use's block will be considered to be below it. void RewriteUse(Use &U); private: |