[Coverage][Expansion] handle nested macros in scratch space (llvm#89869)

The problematic program is as follows:

```shell

void f(void) {
    PRE(a) && 0;
}

int main(void) { return 0; }
```

in which after token concatenation (`##`), there's another nested macro
`pre_a`.

Currently only the outer expansion region will be produced. ([compiler
explorer
link](https://godbolt.org/#g:!((g:!((g:!((h:codeEditor,i:(filename:'1',fontScale:14,fontUsePx:'0',j:1,lang:___c,selection:(endColumn:29,endLineNumber:8,positionColumn:29,positionLineNumber:8,selectionStartColumn:29,selectionStartLineNumber:8,startColumn:29,startLineNumber:8),source:'%23define+pre_a+0%0A%23define+PRE(x)+pre_%23%23x%0A%0Avoid+f(void)+%7B%0A++++PRE(a)+%26%26+0%3B%0A%7D%0A%0Aint+main(void)+%7B+return+0%3B+%7D'),l:'5',n:'0',o:'C+source+%231',t:'0')),k:51.69491525423727,l:'4',n:'0',o:'',s:0,t:'0'),(g:!((g:!((h:compiler,i:(compiler:cclang_assertions_trunk,filters:(b:'0',binary:'1',binaryObject:'1',commentOnly:'0',debugCalls:'1',demangle:'0',directives:'0',execute:'0',intel:'0',libraryCode:'1',trim:'1',verboseDemangling:'0'),flagsViewOpen:'1',fontScale:14,fontUsePx:'0',j:2,lang:___c,libs:!(),options:'-fprofile-instr-generate+-fcoverage-mapping+-fcoverage-mcdc+-Xclang+-dump-coverage-mapping+',overrides:!(),selection:(endColumn:1,endLineNumber:1,positionColumn:1,positionLineNumber:1,selectionStartColumn:1,selectionStartLineNumber:1,startColumn:1,startLineNumber:1),source:1),l:'5',n:'0',o:'+x86-64+clang+(assertions+trunk)+(Editor+%231)',t:'0')),k:34.5741843594503,l:'4',m:28.903654485049834,n:'0',o:'',s:0,t:'0'),(g:!((h:output,i:(compilerName:'x86-64+clang+(trunk)',editorid:1,fontScale:14,fontUsePx:'0',j:2,wrap:'1'),l:'5',n:'0',o:'Output+of+x86-64+clang+(assertions+trunk)+(Compiler+%232)',t:'0')),header:(),l:'4',m:71.09634551495017,n:'0',o:'',s:0,t:'0')),k:48.30508474576271,l:'3',n:'0',o:'',t:'0')),l:'2',m:100,n:'0',o:'',t:'0')),version:4))

```text
f:
  File 0, 4:14 -> 6:2 = #0
  Decision,File 0, 5:5 -> 5:16 = M:0, C:2
  Expansion,File 0, 5:5 -> 5:8 = #0 (Expanded file = 1)
  File 0, 5:15 -> 5:16 = llvm#1
  Branch,File 0, 5:15 -> 5:16 = 0, 0 [2,0,0]
  File 1, 2:16 -> 2:23 = #0
  File 2, 1:15 -> 1:16 = #0
  File 2, 1:15 -> 1:16 = #0
  Branch,File 2, 1:15 -> 1:16 = 0, 0 [1,2,0]
```

The inner expansion region isn't produced because:

1. In the range-based for loop quoted below, each sloc is processed and
possibly emit a corresponding expansion region.
2. For our sloc in question, its direct parent returned by
`getIncludeOrExpansionLoc()` is a `<scratch space>`, because that's how
`##` is processed.

https://github.com/llvm/llvm-project/blob/88b6186af3908c55b357858eb348b5143f21c289/clang/lib/CodeGen/CoverageMappingGen.cpp#L518-L520

3. This `<scratch space>` cannot be found in the FileID mapping so
`ParentFileID` will be assigned an `std::nullopt`

https://github.com/llvm/llvm-project/blob/88b6186af3908c55b357858eb348b5143f21c289/clang/lib/CodeGen/CoverageMappingGen.cpp#L521-L526

4. As a result this iteration of for loop finishes early and no
expansion region is added for the sloc.

This problem gets worse with MC/DC: as the example shows, there's a
branch from File 2 but File 2 itself is missing. This will trigger
assertion failures.

The fix is more or less a workaround and takes a similar approach as

~~Depends on llvm#89573.~~ This includes llvm#89573. Kudos to @chapuni!
This and llvm#89573 together fix llvm#87000: I tested locally, both the reduced
program and my original use case (fwiw, Linux kernel) can run
successfully.

---------

Co-authored-by: NAKAMURA Takumi <[email protected]>

llvmorg-19-init-12274-gf9e9e599c013

Author: whentojump

clang/lib/CodeGen/CoverageMappingGen.cpp

@@ -279,10 +279,36 @@ class CoverageMappingBuilder {
     return SM.getLocForEndOfFile(SM.getFileID(Loc));
   }
 
-  /// Find out where the current file is included or macro is expanded.
-  SourceLocation getIncludeOrExpansionLoc(SourceLocation Loc) {
-    return Loc.isMacroID() ? SM.getImmediateExpansionRange(Loc).getBegin()
-                           : SM.getIncludeLoc(SM.getFileID(Loc));
+  /// Find out where a macro is expanded. If the immediate result is a
+  /// <scratch space>, keep looking until the result isn't. Return a pair of
+  /// \c SourceLocation. The first object is always the begin sloc of found
+  /// result. The second should be checked by the caller: if it has value, it's
+  /// the end sloc of the found result. Otherwise the while loop didn't get
+  /// executed, which means the location wasn't changed and the caller has to
+  /// learn the end sloc from somewhere else.
+  std::pair<SourceLocation, std::optional<SourceLocation>>
+  getNonScratchExpansionLoc(SourceLocation Loc) {
+    std::optional<SourceLocation> EndLoc = std::nullopt;
+    while (Loc.isMacroID() &&
+           SM.isWrittenInScratchSpace(SM.getSpellingLoc(Loc))) {
+      auto ExpansionRange = SM.getImmediateExpansionRange(Loc);
+      Loc = ExpansionRange.getBegin();
+      EndLoc = ExpansionRange.getEnd();
+    }
+    return std::make_pair(Loc, EndLoc);
+  }
+
+  /// Find out where the current file is included or macro is expanded. If
+  /// \c AcceptScratch is set to false, keep looking for expansions until the
+  /// found sloc is not a <scratch space>.
+  SourceLocation getIncludeOrExpansionLoc(SourceLocation Loc,
+                                          bool AcceptScratch = true) {
+    if (!Loc.isMacroID())
+      return SM.getIncludeLoc(SM.getFileID(Loc));
+    Loc = SM.getImmediateExpansionRange(Loc).getBegin();
+    if (AcceptScratch)
+      return Loc;
+    return getNonScratchExpansionLoc(Loc).first;
   }
 
   /// Return true if \c Loc is a location in a built-in macro.
@@ -329,6 +355,15 @@ class CoverageMappingBuilder {
     for (auto &Region : SourceRegions) {
       SourceLocation Loc = Region.getBeginLoc();
 
+      // Replace Region with its definition if it is in <scratch space>.
+      auto NonScratchExpansionLoc = getNonScratchExpansionLoc(Loc);
+      auto EndLoc = NonScratchExpansionLoc.second;
+      if (EndLoc.has_value()) {
+        Loc = NonScratchExpansionLoc.first;
+        Region.setStartLoc(Loc);
+        Region.setEndLoc(EndLoc.value());
+      }
+
       // Replace Loc with FileLoc if it is expanded with system headers.
       if (!SystemHeadersCoverage && SM.isInSystemMacro(Loc)) {
         auto BeginLoc = SM.getSpellingLoc(Loc);
@@ -514,7 +549,7 @@ class CoverageMappingBuilder {
     SourceRegionFilter Filter;
     for (const auto &FM : FileIDMapping) {
       SourceLocation ExpandedLoc = FM.second.second;
-      SourceLocation ParentLoc = getIncludeOrExpansionLoc(ExpandedLoc);
+      SourceLocation ParentLoc = getIncludeOrExpansionLoc(ExpandedLoc, false);
       if (ParentLoc.isInvalid())
         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 +1,65 @@
+// 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 pre_foo pre_a
+
+// CHECK: pre1:
+int pre1(int pre_a, int b_post) {
+  // CHECK: Decision,File 0, [[@LINE+3]]:11 -> [[@LINE+4]]:20 = M:0, C:2
+  // CHECK: Expansion,File 0, [[@LINE+2]]:11 -> [[@LINE+2]]:14 = #0 (Expanded file = 1)
+  // CHECK: Branch,File 0, [[@LINE+2]]:14 -> [[@LINE+2]]:20 = #2, (#1 - #2) [2,0,0]
+  return (PRE(foo)
+          && b_post);
+  // CHECK: Expansion,File 1, 17:16 -> 17:20 = #0 (Expanded file = 2)
+  // CHECK: Branch,File 2, 29:17 -> 29:22 = #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]
+}
+
+#define bar_post b_post
+
+// CHECK: post1:
+int post1(int pre_a, int b_post) {
+  // CHECK: Decision,File 0, [[@LINE+3]]:11 -> [[@LINE+4]]:18 = M:0, C:2
+  // CHECK: Branch,File 0, [[@LINE+2]]:11 -> [[@LINE+2]]:16 = (#0 - #1), #1 [1,0,2]
+  // CHECK: Expansion,File 0, [[@LINE+2]]:14 -> [[@LINE+2]]:18 = 0 (Expanded file = 1)
+  return (pre_a
+          || POST(bar));
+  // CHECK: Expansion,File 1, 42:17 -> 42:18 = #1 (Expanded file = 2)
+  // CHECK: Branch,File 2, 54:18 -> 54:24 = (#1 - #2), #2 [2,0,0]
+}