diff options
| -rw-r--r-- | include/llvm/Analysis/Loads.h | 40 | ||||
| -rw-r--r-- | lib/Analysis/Loads.cpp | 19 |
2 files changed, 25 insertions, 34 deletions
diff --git a/include/llvm/Analysis/Loads.h b/include/llvm/Analysis/Loads.h index 9d24b7b2928..08381b64823 100644 --- a/include/llvm/Analysis/Loads.h +++ b/include/llvm/Analysis/Loads.h @@ -61,24 +61,34 @@ bool isSafeToLoadUnconditionally(Value *V, unsigned Align, /// to scan in the block, used by FindAvailableLoadedValue(). extern cl::opt<unsigned> DefMaxInstsToScan; -/// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at -/// the instruction before ScanFrom) checking to see if we have the value at -/// the memory address *Ptr locally available within a small number of -/// instructions. If the value is available, return it. +/// \brief Scan backwards to see if we have the value of the given load +/// available locally within a small number of instructions. /// -/// If not, return the iterator for the last validated instruction that the -/// value would be live through. If we scanned the entire block and didn't -/// find something that invalidates *Ptr or provides it, ScanFrom would be -/// left at begin() and this returns null. ScanFrom could also be left +/// You can use this function to scan across multiple blocks: after you call +/// this function, if ScanFrom points at the beginning of the block, it's safe +/// to continue scanning the predecessors. /// -/// MaxInstsToScan specifies the maximum instructions to scan in the block. -/// If it is set to 0, it will scan the whole block. You can also optionally -/// specify an alias analysis implementation, which makes this more precise. +/// Note that performing load CSE requires special care to make sure the +/// metadata is set appropriately. In particular, aliasing metadata needs +/// to be merged. (This doesn't matter for store-to-load forwarding because +/// the only relevant load gets deleted.) /// -/// If AATags is non-null and a load or store is found, the AA tags from the -/// load or store are recorded there. If there are no AA tags or if no access -/// is found, it is left unmodified. -Value *FindAvailableLoadedValue(LoadInst *Load, BasicBlock *ScanBB, +/// \param Load The load we want to replace. +/// \param ScanBB The basic block to scan. FIXME: This is redundant. +/// \param [in,out] ScanFrom The location to start scanning from. When this +/// function returns, it points at the last instruction scanned. +/// \param MaxInstsToScan The maximum number of instructions to scan. If this +/// is zero, the whole block will be scanned. +/// \param AA Optional pointer to alias analysis, to make the scan more +/// precise. +/// \param [out] AATags The aliasing metadata for the operation which produced +/// the value. FIXME: This is basically useless. +/// \param [out] isLoadCSE Whether the returned value is a load from the same +/// location in memory, as opposed to the value operand of a store. +/// +/// \returns The found value, or nullptr if no value is found. +Value *FindAvailableLoadedValue(LoadInst *Load, + BasicBlock *ScanBB, BasicBlock::iterator &ScanFrom, unsigned MaxInstsToScan = DefMaxInstsToScan, AliasAnalysis *AA = nullptr, diff --git a/lib/Analysis/Loads.cpp b/lib/Analysis/Loads.cpp index 7d3fd5951eb..179b79ebcee 100644 --- a/lib/Analysis/Loads.cpp +++ b/lib/Analysis/Loads.cpp @@ -300,25 +300,6 @@ llvm::DefMaxInstsToScan("available-load-scan-limit", cl::init(6), cl::Hidden, "to scan backward from a given instruction, when searching for " "available loaded value")); -/// \brief Scan the ScanBB block backwards to see if we have the value at the -/// memory address *Ptr locally available within a small number of instructions. -/// -/// The scan starts from \c ScanFrom. \c MaxInstsToScan specifies the maximum -/// instructions to scan in the block. If it is set to \c 0, it will scan the whole -/// block. -/// -/// If the value is available, this function returns it. If not, it returns the -/// iterator for the last validated instruction that the value would be live -/// through. If we scanned the entire block and didn't find something that -/// invalidates \c *Ptr or provides it, \c ScanFrom is left at the last -/// instruction processed and this returns null. -/// -/// You can also optionally specify an alias analysis implementation, which -/// makes this more precise. -/// -/// If \c AATags is non-null and a load or store is found, the AA tags from the -/// load or store are recorded there. If there are no AA tags or if no access is -/// found, it is left unmodified. Value *llvm::FindAvailableLoadedValue(LoadInst *Load, BasicBlock *ScanBB, BasicBlock::iterator &ScanFrom, unsigned MaxInstsToScan, |