[MC/DC][Coverage] Workaround for ## conditions

A synthesized identifier with `##` is emitted to `<scratch space>`.
`llvm-cov` cannot handle `<scratch space> since it doesn't have actual files.

As a workaround, peel `<scratch space>` to the actual definition if the definition is present.

This affects predefined built-in macros, like __LINE__.

Fixes #87000

Author: chapuni

clang/lib/CodeGen/CoverageMappingGen.cpp

@@ -339,8 +339,18 @@ class CoverageMappingBuilder {
 
     llvm::SmallSet<FileID, 8> Visited;
     SmallVector<std::pair<SourceLocation, unsigned>, 8> FileLocs;
-    for (const auto &Region : SourceRegions) {
+    for (auto &Region : SourceRegions) {
       SourceLocation Loc = Region.getBeginLoc();
+
+      // Replace Region with its definition if it is in <scratch space>.
+      while (Loc.isMacroID() &&
+             SM.isWrittenInScratchSpace(SM.getSpellingLoc(Loc))) {
+        auto ExpansionRange = SM.getImmediateExpansionRange(Loc);
+        Loc = ExpansionRange.getBegin();
+        Region.setStartLoc(Loc);
+        Region.setEndLoc(ExpansionRange.getEnd());
+      }
+
       FileID File = SM.getFileID(Loc);
       if (!Visited.insert(File).second)
         continue;

clang/test/CoverageMapping/builtinmacro.c

@@ -4,7 +4,7 @@
 
 // CHECK: filename
 const char *filename (const char *name) { // CHECK-NEXT: File 0, [[@LINE]]:41 -> [[@LINE+3]]:2 = #0
-  static const char this_file[] = __FILE__;
+  static const char this_file[] = __FILE__; // CHECK-NEXT: File 0, [[@LINE]]:35 -> [[@LINE]]:35 = #0
   return this_file;
 }
 

clang/test/CoverageMapping/macros.c

@@ -80,12 +80,14 @@ void func7(void) { // CHECK-NEXT: File 0, [[@LINE]]:18 -> [[@LINE+6]]:2 = #0
   int kk,ll;       // CHECK-NEXT: File 0, [[@LINE+1]]:7 -> [[@LINE+1]]:8 = #0
   if (k)           // CHECK-NEXT: Branch,File 0, [[@LINE]]:7 -> [[@LINE]]:8 = #1
     m(k);          // CHECK-NEXT: Gap,File 0, [[@LINE-1]]:9 -> [[@LINE]]:5 = #1
-  else             // CHECK-NEXT: Expansion,File 0, [[@LINE-1]]:5 -> [[@LINE-1]]:6 = #0
+  else             // CHECK-NEXT: Expansion,File 0, [[@LINE-1]]:5 -> [[@LINE-1]]:6 = #1
     l = m(l);      // CHECK-NEXT: Gap,File 0, [[@LINE-2]]:7 -> [[@LINE]]:5 = (#0 - #1)
 }                  // CHECK-NEXT: File 0, [[@LINE-1]]:5 -> [[@LINE-1]]:10 = (#0 - #1)
                    // CHECK-NEXT: Expansion,File 0, [[@LINE-2]]:9 -> [[@LINE-2]]:10 = (#0 - #1)
-                   // CHECK-NEXT: File 1, [[@LINE-9]]:14 -> [[@LINE-9]]:18 = #0
-                   // CHECK-NEXT: File 2, [[@LINE-10]]:14 -> [[@LINE-10]]:15 = (#0 - #1)
+                   // CHECK-NEXT: File 1, [[@LINE-9]]:14 -> [[@LINE-9]]:17 = #1
+                   // CHECK-NEXT: File 1, [[@LINE-10]]:14 -> [[@LINE-10]]:18 = #0
+                   // CHECK-NEXT: File 2, [[@LINE-11]]:14 -> [[@LINE-11]]:17 = (#0 - #1)
+                   // CHECK-NEXT: File 2, [[@LINE-12]]:14 -> [[@LINE-12]]:15 = (#0 - #1)
 
 int main(int argc, const char *argv[]) {
   func();

clang/test/CoverageMapping/mcdc-scratch-space.c

@@ -0,0 +1,39 @@
+// RUN: %clang_cc1 -triple %itanium_abi_triple -std=c99 -fcoverage-mcdc -fprofile-instrument=clang -fcoverage-mapping -dump-coverage-mapping -emit-llvm-only %s | FileCheck %s
+
+// CHECK: builtin_macro0:
+int builtin_macro0(int a) {
+  // CHECK: Decision,File 0, [[@LINE+1]]:11 -> [[@LINE+2]]:15 = M:0, C:2
+  return (__LINE__ // CHECK: Branch,File 0, [[@LINE]]:11 -> [[@LINE]]:11 = 0, 0 [1,2,0]
+          && a); //   CHECK: Branch,File 0, [[@LINE]]:14 -> [[@LINE]]:15 = #2, (#1 - #2) [2,0,0]
+}
+
+// CHECK: builtin_macro1:
+int builtin_macro1(int a) {
+  // CHECK: Decision,File 0, [[@LINE+1]]:11 -> [[@LINE+2]]:22 = M:0, C:2
+  return (a // CHECK: Branch,File 0, [[@LINE]]:11 -> [[@LINE]]:12 = (#0 - #1), #1 [1,0,2]
+          || __LINE__); // CHECK: Branch,File 0, [[@LINE]]:14 -> [[@LINE]]:14 = 0, 0 [2,0,0]
+}
+
+#define PRE(x) pre_##x
+
+// CHECK: pre0:
+int pre0(int pre_a, int b_post) {
+  // CHECK: Decision,File 0, [[@LINE+2]]:11 -> [[@LINE+3]]:20 = M:0, C:2
+  // CHECK: Expansion,File 0, [[@LINE+1]]:11 -> [[@LINE+1]]:14 = #0 (Expanded file = 1)
+  return (PRE(a)
+          && b_post);
+  // CHECK: Branch,File 0, [[@LINE-1]]:14 -> [[@LINE-1]]:20 = #2, (#1 - #2) [2,0,0]
+  // CHECK: Branch,File 1, [[@LINE-9]]:16 -> [[@LINE-9]]:22 = #1, (#0 - #1) [1,2,0]
+}
+
+#define POST(x) x##_post
+
+// CHECK: post0:
+int post0(int pre_a, int b_post) {
+  // CHECK: Decision,File 0, [[@LINE+2]]:11 -> [[@LINE+3]]:18 = M:0, C:2
+  // CHECK: Branch,File 0, [[@LINE+1]]:11 -> [[@LINE+1]]:16 = (#0 - #1), #1 [1,0,2]
+  return (pre_a
+          || POST(b));
+  // CHECK: Expansion,File 0, [[@LINE-1]]:14 -> [[@LINE-1]]:18 = #1 (Expanded file = 1)
+  // CHECK: Branch,File 1, [[@LINE-9]]:17 -> [[@LINE-9]]:20 = (#1 - #2), #2 [2,0,0]
+}