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Properly handle cases where a predecessor of the block being queried on is unreachable.

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This fixes PR2503, though we should also fix other passes not to emit this kind of code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52946 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2008-07-01 00:40:58 +00:00
parent f4f9c4f1cf
commit c4b871c650
1 changed files with 13 additions and 0 deletions
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13
lib/Analysis/MemoryDependenceAnalysis.cpp
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@ -19,6 +19,7 @@
#include "llvm/Instructions.h" #include "llvm/Instructions.h"
#include "llvm/Function.h" #include "llvm/Function.h"
#include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Support/CFG.h" #include "llvm/Support/CFG.h"
#include "llvm/Support/CommandLine.h" #include "llvm/Support/CommandLine.h"
#include "llvm/Target/TargetData.h" #include "llvm/Target/TargetData.h"
@ -82,6 +83,7 @@ void MemoryDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll(); AU.setPreservesAll();
AU.addRequiredTransitive<AliasAnalysis>(); AU.addRequiredTransitive<AliasAnalysis>();
AU.addRequiredTransitive<TargetData>(); AU.addRequiredTransitive<TargetData>();
AU.addRequiredTransitive<DominatorTree>();
} }
/// getCallSiteDependency - Private helper for finding the local dependencies /// getCallSiteDependency - Private helper for finding the local dependencies
@ -222,6 +224,17 @@ void MemoryDependenceAnalysis::nonLocalHelper(Instruction* query,
continue; continue;
} }
// Don't recur upwards if the current block is unreachable.
// Instead, mark it as having no dependency on this path,
// which will block optzns from occuring. For this reason,
// eliminating unreachable blocks before running a memdep
// based optimization is recommended.
DominatorTree& DT = getAnalysis<DominatorTree>();
if (!DT.isReachableFromEntry(BB)) {
resp.insert(std::make_pair(BB, None));
continue;
}
// If we didn't find anything, recurse on the precessors of this block // If we didn't find anything, recurse on the precessors of this block
// Only do this for blocks with a small number of predecessors. // Only do this for blocks with a small number of predecessors.
bool predOnStack = false; bool predOnStack = false;