Build up statistics about the work done for analysis based warnings.

Special detail is added for uninitialized variable analysis as this has
serious performance problems than need to be tracked.

Computing some of this data is expensive, for example walking the CFG to
determine its size. To avoid doing that unless the stats data is going
to be used, we thread a bit into the Sema object to track whether
detailed stats should be collected or not. This bit is used to avoid
computations whereever the computations are likely to be more expensive
than checking the state of the flag. Thus, counters are in some cases
unconditionally updated, but the more expensive (and less frequent)
aggregation steps are skipped.

With this patch, we're able to see that for 'gcc.c':
*** Analysis Based Warnings Stats:
232 functions analyzed (0 w/o CFGs).
  7151 CFG blocks built.
  30 average CFG blocks per function.
  1167 max CFG blocks per function.
163 functions analyzed for uninitialiazed variables
  640 variables analyzed.
  3 average variables per function.
  94 max variables per function.
  96409 block visits.
  591 average block visits per function.
  61546 max block visits per function.

And for the reduced testcase in PR10183:
*** Analysis Based Warnings Stats:
98 functions analyzed (0 w/o CFGs).
  8526 CFG blocks built.
  87 average CFG blocks per function.
  7277 max CFG blocks per function.
68 functions analyzed for uninitialiazed variables
  1359 variables analyzed.
  19 average variables per function.
  1196 max variables per function.
  2540494 block visits.
  37360 average block visits per function.
  2536495 max block visits per function.

That last number is the somewhat scary one that indicates the problem in
PR10183.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@134494 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 66 insertions, 2 deletions

diff --git a/lib/Sema/AnalysisBasedWarnings.cpp b/lib/Sema/AnalysisBasedWarnings.cpp
index e560ef8a5c..8a4634df2f 100644
--- a/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/lib/Sema/AnalysisBasedWarnings.cpp
@@ -597,7 +597,11 @@ clang::sema::AnalysisBasedWarnings::Policy::Policy() {
   enableCheckUnreachable = 0;
 }
 
-clang::sema::AnalysisBasedWarnings::AnalysisBasedWarnings(Sema &s) : S(s) {
+clang::sema::AnalysisBasedWarnings::AnalysisBasedWarnings(Sema &s)
+  : S(s),
+    NumFunctionsAnalyzed(0),
+    NumCFGBlocks(0),
+    MaxCFGBlocksPerFunction(0) {
   Diagnostic &D = S.getDiagnostics();
   DefaultPolicy.enableCheckUnreachable = (unsigned)
     (D.getDiagnosticLevel(diag::warn_unreachable, SourceLocation()) !=
@@ -713,8 +717,68 @@ AnalysisBasedWarnings::IssueWarnings(sema::AnalysisBasedWarnings::Policy P,
       != Diagnostic::Ignored) {
     if (CFG *cfg = AC.getCFG()) {
       UninitValsDiagReporter reporter(S);
+      UninitVariablesAnalysisStats stats = {};
       runUninitializedVariablesAnalysis(*cast<DeclContext>(D), *cfg, AC,
-                                        reporter);
+                                        reporter, stats);
+
+      if (S.CollectStats && stats.NumVariablesAnalyzed > 0) {
+        ++NumUninitAnalysisFunctions;
+        NumUninitAnalysisVariables += stats.NumVariablesAnalyzed;
+        NumUninitAnalysisBlockVisits += stats.NumBlockVisits;
+        MaxUninitAnalysisVariablesPerFunction =
+            std::max(MaxUninitAnalysisVariablesPerFunction,
+                     stats.NumVariablesAnalyzed);
+        MaxUninitAnalysisBlockVisitsPerFunction =
+            std::max(MaxUninitAnalysisBlockVisitsPerFunction,
+                     stats.NumBlockVisits);
+      }
+    }
+  }
+
+  // Collect statistics about the CFG if it was built.
+  if (S.CollectStats && AC.isCFGBuilt()) {
+    ++NumFunctionsAnalyzed;
+    if (CFG *cfg = AC.getCFG()) {
+      // If we successfully built a CFG for this context, record some more
+      // detail information about it.
+      unsigned NumBlocks = std::distance(cfg->begin(), cfg->end());
+      NumCFGBlocks += NumBlocks;
+      MaxCFGBlocksPerFunction = std::max(MaxCFGBlocksPerFunction,
+                                         NumBlocks);
+    } else {
+      ++NumFunctionsWithBadCFGs;
     }
   }
 }
+
+void clang::sema::AnalysisBasedWarnings::PrintStats() const {
+  llvm::errs() << "\n*** Analysis Based Warnings Stats:\n";
+
+  unsigned NumCFGsBuilt = NumFunctionsAnalyzed - NumFunctionsWithBadCFGs;
+  unsigned AvgCFGBlocksPerFunction =
+      !NumCFGsBuilt ? 0 : NumCFGBlocks/NumCFGsBuilt;
+  llvm::errs() << NumFunctionsAnalyzed << " functions analyzed ("
+               << NumFunctionsWithBadCFGs << " w/o CFGs).\n"
+               << "  " << NumCFGBlocks << " CFG blocks built.\n"
+               << "  " << AvgCFGBlocksPerFunction
+               << " average CFG blocks per function.\n"
+               << "  " << MaxCFGBlocksPerFunction
+               << " max CFG blocks per function.\n";
+
+  unsigned AvgUninitVariablesPerFunction = !NumUninitAnalysisFunctions ? 0
+      : NumUninitAnalysisVariables/NumUninitAnalysisFunctions;
+  unsigned AvgUninitBlockVisitsPerFunction = !NumUninitAnalysisFunctions ? 0
+      : NumUninitAnalysisBlockVisits/NumUninitAnalysisFunctions;
+  llvm::errs() << NumUninitAnalysisFunctions
+               << " functions analyzed for uninitialiazed variables\n"
+               << "  " << NumUninitAnalysisVariables << " variables analyzed.\n"
+               << "  " << AvgUninitVariablesPerFunction
+               << " average variables per function.\n"
+               << "  " << MaxUninitAnalysisVariablesPerFunction
+               << " max variables per function.\n"
+               << "  " << NumUninitAnalysisBlockVisits << " block visits.\n"
+               << "  " << AvgUninitBlockVisitsPerFunction
+               << " average block visits per function.\n"
+               << "  " << MaxUninitAnalysisBlockVisitsPerFunction
+               << " max block visits per function.\n";
+}