Merging rr261430:

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r261430 | joerg | 2016-02-20 12:24:44 +0100 (Sat, 20 Feb 2016) | 15 lines

When MemoryDependenceAnalysis hits a CFG with many transparent blocks,
the algorithm easily degrades into quadratic memory and time complexity.
The easiest example is a long chain of BBs that don't otherwise use a
location. The caching will add an entry for every intermediate block and
limiting the number of results doesn't help as no results are produced
until a definition is found.

Introduce a limit similar to the existing instructions-per-block limit.
This limit counts the total number of blocks checked. If the limit is
reached, entries are considered unknown. The initial value is 1000,
which avoids regressions for normal sized functions while still
limiting edge cases to reasnable memory consumption and execution time.

Differential Revision: http://reviews.llvm.org/D16123

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_38@271394 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index 6918360536a300b58ccdb8dca5e5dc6676092348..85fa37f64ceec74753b5c8bb7a7182deecb3614c 100644 (file)
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -57,6 +57,11 @@ static cl::opt<unsigned> BlockScanLimit(
     cl::desc("The number of instructions to scan in a block in memory "
              "dependency analysis (default = 100)"));
 
+static cl::opt<unsigned> BlockNumberLimit(
+    "memdep-block-number-limit", cl::Hidden, cl::init(1000),
+    cl::desc("The number of blocks to scan during memory "
+             "dependency analysis (default = 1000)"));
+
 // Limit on the number of memdep results to process.
 static const unsigned int NumResultsLimit = 100;
 
@@ -1246,6 +1251,8 @@ bool MemoryDependenceAnalysis::getNonLocalPointerDepFromBB(
   // won't get any reuse from currently inserted values, because we don't
   // revisit blocks after we insert info for them.
   unsigned NumSortedEntries = Cache->size();
+  unsigned WorklistEntries = BlockNumberLimit;
+  bool GotWorklistLimit = false;
   DEBUG(AssertSorted(*Cache));
 
   while (!Worklist.empty()) {
@@ -1324,6 +1331,15 @@ bool MemoryDependenceAnalysis::getNonLocalPointerDepFromBB(
           goto PredTranslationFailure;
         }
       }
+      if (NewBlocks.size() > WorklistEntries) {
+        // Make sure to clean up the Visited map before continuing on to
+        // PredTranslationFailure.
+        for (unsigned i = 0; i < NewBlocks.size(); i++)
+          Visited.erase(NewBlocks[i]);
+        GotWorklistLimit = true;
+        goto PredTranslationFailure;
+      }
+      WorklistEntries -= NewBlocks.size();
       Worklist.append(NewBlocks.begin(), NewBlocks.end());
       continue;
     }
@@ -1469,18 +1485,22 @@ bool MemoryDependenceAnalysis::getNonLocalPointerDepFromBB(
     if (SkipFirstBlock)
       return true;
 
-    for (NonLocalDepInfo::reverse_iterator I = Cache->rbegin(); ; ++I) {
-      assert(I != Cache->rend() && "Didn't find current block??");
-      if (I->getBB() != BB)
+    bool foundBlock = false;
+    for (NonLocalDepEntry &I: llvm::reverse(*Cache)) {
+      if (I.getBB() != BB)
         continue;
 
-      assert((I->getResult().isNonLocal() || !DT->isReachableFromEntry(BB)) &&
+      assert((GotWorklistLimit || I.getResult().isNonLocal() || \
+              !DT->isReachableFromEntry(BB)) &&
              "Should only be here with transparent block");
-      I->setResult(MemDepResult::getUnknown());
-      Result.push_back(NonLocalDepResult(I->getBB(), I->getResult(),
+      foundBlock = true;
+      I.setResult(MemDepResult::getUnknown());
+      Result.push_back(NonLocalDepResult(I.getBB(), I.getResult(),
                                          Pointer.getAddr()));
       break;
     }
+    (void)foundBlock;
+    assert((foundBlock || GotWorklistLimit) && "Current block not in cache?");
   }
 
   // Okay, we're done now.  If we added new values to the cache, re-sort it.

diff --git a/utils/release/merge.sh b/utils/release/merge.sh
index 93e08c7ce135735064cf68697676bccf5025beb1..b48932248347dddcab78eb189deb11679c537006 100755 (executable)
--- a/utils/release/merge.sh
+++ b/utils/release/merge.sh
@@ -17,12 +17,14 @@ set -e
 rev=""
 proj=""
 revert="no"
+srcdir=""
 
-function usage() {
+usage() {
     echo "usage: `basename $0` [OPTIONS]"
     echo "  -proj PROJECT  The project to merge the result into"
     echo "  -rev NUM       The revision to merge into the project"
     echo "  -revert        Revert rather than merge the commit"
+    echo "  -srcdir        The root of the project checkout"
 }
 
 while [ $# -gt 0 ]; do
@@ -35,6 +37,10 @@ while [ $# -gt 0 ]; do
             shift
             proj=$1
             ;;
+        --srcdir | -srcdir | -s)
+            shift
+            srcdir=$1
+            ;;
         -h | -help | --help )
             usage
             ;;
@@ -51,6 +57,10 @@ while [ $# -gt 0 ]; do
     shift
 done
 
+if [ -z "$srcdir" ]; then
+    srcdir="$proj.src"
+fi
+
 if [ "x$rev" = "x" -o "x$proj" = "x" ]; then
     echo "error: need to specify project and revision"
     echo
@@ -72,7 +82,7 @@ else
 fi
 svn log -c $rev http://llvm.org/svn/llvm-project/$proj/trunk >> $tempfile 2>&1
 
-cd $proj.src
+cd "$srcdir"
 echo "# Updating tree"
 svn up