diff options
Diffstat (limited to 'lib/Transforms/Scalar/GVN.cpp')
| -rw-r--r-- | lib/Transforms/Scalar/GVN.cpp | 29 |
1 files changed, 26 insertions, 3 deletions
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp index 673d38b7f3ae6..f4a989844478f 100644 --- a/lib/Transforms/Scalar/GVN.cpp +++ b/lib/Transforms/Scalar/GVN.cpp @@ -37,6 +37,7 @@ #include "llvm/Support/Compiler.h" #include "llvm/Support/Debug.h" #include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Local.h" #include <cstdio> using namespace llvm; @@ -48,7 +49,7 @@ STATISTIC(NumPRELoad, "Number of loads PRE'd"); static cl::opt<bool> EnablePRE("enable-pre", cl::init(true), cl::Hidden); -cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); +static cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); //===----------------------------------------------------------------------===// // ValueTable Class @@ -952,8 +953,14 @@ bool GVN::processNonLocalLoad(LoadInst *LI, // If we had a phi translation failure, we'll have a single entry which is a // clobber in the current block. Reject this early. - if (Deps.size() == 1 && Deps[0].second.isClobber()) + if (Deps.size() == 1 && Deps[0].second.isClobber()) { + DEBUG( + DOUT << "GVN: non-local load "; + WriteAsOperand(*DOUT.stream(), LI); + DOUT << " is clobbered by " << *Deps[0].second.getInst(); + ); return false; + } // Filter out useless results (non-locals, etc). Keep track of the blocks // where we have a value available in repl, also keep track of whether we see @@ -1069,6 +1076,7 @@ bool GVN::processNonLocalLoad(LoadInst *LI, BasicBlock *TmpBB = LoadBB; bool isSinglePred = false; + bool allSingleSucc = true; while (TmpBB->getSinglePredecessor()) { isSinglePred = true; TmpBB = TmpBB->getSinglePredecessor(); @@ -1078,6 +1086,8 @@ bool GVN::processNonLocalLoad(LoadInst *LI, return false; if (Blockers.count(TmpBB)) return false; + if (TmpBB->getTerminator()->getNumSuccessors() != 1) + allSingleSucc = false; } assert(TmpBB); @@ -1154,7 +1164,20 @@ bool GVN::processNonLocalLoad(LoadInst *LI, << UnavailablePred->getName() << "': " << *LI); return false; } - + + // Make sure it is valid to move this load here. We have to watch out for: + // @1 = getelementptr (i8* p, ... + // test p and branch if == 0 + // load @1 + // It is valid to have the getelementptr before the test, even if p can be 0, + // as getelementptr only does address arithmetic. + // If we are not pushing the value through any multiple-successor blocks + // we do not have this case. Otherwise, check that the load is safe to + // put anywhere; this can be improved, but should be conservatively safe. + if (!allSingleSucc && + !isSafeToLoadUnconditionally(LoadPtr, UnavailablePred->getTerminator())) + return false; + // Okay, we can eliminate this load by inserting a reload in the predecessor // and using PHI construction to get the value in the other predecessors, do // it. |