[Coverage] Fix crash in VisitIfStmt

[vsk]

Summary

When handling 'if' statements, we crash if the condition and the consequent
branch are spanned by a single macro expansion.

The crash occurs because of a sanity 'reset' in popRegions(): if an expansion
exactly spans an entire region, we set MostRecentLocation to the start of the
expansion (its 'include location'). This ensures we don't handleFileExit()
ourselves out of the expansion before we're done processing all of the regions
within it. This is tested in test/CoverageMapping/macro-expressions.c.

This causes a problem when an expansion spans both the condition and the
consequent branch of an 'if' statement. MostRecentLocation is updated to the
start of the 'if' statement in popRegions(), so the file for the expansion
isn't exited by the time we're done handling the statement. We then crash with
'fatal: File exit not handled before popRegions'.

The fix for this is to detect these kinds of expansions, and conservatively
update MostRecentLocation to the end of expansion region containing the
conditional. I've added tests to make sure we don't have the same problem with
other kinds of statements.

rdar://problem/23630316

[vsk]

• Made the check a bit more general by moving it to propagateCounts.
• Added 3 more tests.

[vsk]

• Check that we don't crash on a nested 'STMT' test case.

lib/CodeGen/CoverageMappingGen.cpp

struct CounterCoverageMappingBuilder
   }
 
   /// \brief Propagate counts through the children of \c S.
   Counter propagateCounts(Counter TopCount, const Stmt *S) {
     size_t Index = pushRegion(TopCount, getStart(S), getEnd(S));
     Visit(S);
     Counter ExitCount = getRegion().getCounter();
     popRegions(Index);
+
+    // The statement may be spanned by an expansion. Make sure we handle a file
+    // exit out of this expansion before moving to the next statement.
+    if (SM.isBeforeInTranslationUnit(getStart(S), S->getLocStart()))
+      MostRecentLocation = getEnd(S);
+
     return ExitCount;
   }
 
   /// \brief Adjust the most recently visited location to \c EndLoc.
   ///
   /// This should be used after visiting any statements in non-source order.
   void adjustForOutOfOrderTraversal(SourceLocation EndLoc) {
     MostRecentLocation = EndLoc;

test/CoverageMapping/macro-expressions.cpp

 // RUN: %clang_cc1 -std=c++11 -fprofile-instrument=clang -fcoverage-mapping -dump-coverage-mapping -emit-llvm-only -main-file-name macro-expressions.cpp %s | FileCheck %s
 
 #define EXPR(x) (x)
 #define NEXPR(x) (!x)
 #define DECL(T, x) T x
 #define ASSIGN(x, y) x = y
 #define LT(x, y) x < y
 #define INC(x) ++x
 #define ARR(T, x, y, z) (T[3]){x, y, z}
 
 #define PRI_64_LENGTH_MODIFIER "ll"
 #define PRIo64 PRI_64_LENGTH_MODIFIER "o"
 #define PRIu64 PRI_64_LENGTH_MODIFIER "u"
 
+#define STMT(s) s
+
+void fn1() {
+  STMT(if (1));
+  STMT(while (1));
+  STMT(for (;;));
+  STMT(if) (1);
+  STMT(while) (1);
+  STMT(for) (;;);
+  if (1)
+    STMT(if (1)) 0;
+  if (1)
+    STMT(while (1)) 0;
+  if (1)
+    STMT(for (;;)) 0;
+  while (1)
+    STMT(if (1)) 0;
+  while (1)
+    STMT(while (1)) 0;
+  while (1)
+    STMT(for (;;)) 0;
+  for (;;)
+    STMT(if (1)) 0;
+  for (;;)
+    STMT(while (1)) 0;
+  for (;;)
+    STMT(for (;;)) 0;
+}
+
+void STMT(fn2()) {
+}
+
+void STMT(fn3)() {
+}
+
 // CHECK: foo
 // CHECK-NEXT: File 0, [[@LINE+1]]:17 -> {{[0-9]+}}:2 = #0
 void foo(int i) {
   // CHECK-NEXT: File 0, [[@LINE+2]]:7 -> [[@LINE+2]]:8 = #0
   // CHECK-NEXT: File 0, [[@LINE+1]]:10 -> [[@LINE+1]]:12 = #1
   if (0) {}
 
   // CHECK-NEXT: Expansion,File 0, [[@LINE+2]]:7 -> [[@LINE+2]]:11 = #0