[SanitizerCoverage] Don't add instrumentation to unreachable blocks.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241127 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Instrumentation/SanitizerCoverage.cpp

@@ -375,6 +375,13 @@ void SanitizerCoverageModule::SetNoSanitizeMetadata(Instruction *I) {
 
 void SanitizerCoverageModule::InjectCoverageAtBlock(Function &F, BasicBlock &BB,
                                                     bool UseCalls) {
+  // Don't insert coverage for unreachable blocks: we will never call
+  // __sanitizer_cov() for them, so counting them in
+  // NumberOfInstrumentedBlocks() might complicate calculation of code coverage
+  // percentage. Also, unreachable instructions frequently have no debug
+  // locations.
+  if (isa<UnreachableInst>(BB.getTerminator()))
+    return;
   BasicBlock::iterator IP = BB.getFirstInsertionPt(), BE = BB.end();
   // Skip static allocas at the top of the entry block so they don't become
   // dynamic when we split the block.  If we used our optimized stack layout,

test/Instrumentation/SanitizerCoverage/coverage.ll

@@ -119,3 +119,12 @@ entry:
 ; CHECK4: call void @__sanitizer_cov_indir_call16({{.*}},[[CACHE:.*]])
 ; CHECK4-NOT: call void @__sanitizer_cov_indir_call16({{.*}},[[CACHE]])
 ; CHECK4: ret void
+
+define void @call_unreachable() uwtable sanitize_address {
+entry:
+  unreachable
+}
+
+; CHECK4-LABEL: define void @call_unreachable
+; CHECK4-NOT: __sanitizer_cov
+; CHECK4: unreachable