[clang][CoverageMapping] do not emit gap when either end is an ImplicitValueInitExpr

[whentojump]

Fixes #86998

Two compiler explorer examples: 1, 2

Cause:

1. When visiting AST and generating mapping regions, a region terminator (like break and goto) is likely followed by a stmt with <invalid sloc> (like ImplicitValueInitExpr).

2. Because a terminator is seen, the below branch will be executed when visiting the 2nd stmt:

   llvm-project/clang/lib/CodeGen/CoverageMappingGen.cpp

   Lines 1375 to 1376 in e6c3289

   	if (LastStmt && HasTerminateStmt && !isa<AttributedStmt>(Child)) {
   	auto Gap = findGapAreaBetween(getEnd(LastStmt), getStart(Child));

3. However, the 2nd stmt doesn't have a valid source location and will fail some assertions in findGapAreaBetween().

[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-codegen

Author: Wentao Zhang (whentojump)

Changes

Fixes #86998

Two compiler explorer examples: 1, 2

Cause:

1. When visiting AST and generating mapping regions, a region terminator (like break and goto) is likely followed by a stmt with <invalid sloc> (like ImplicitValueInitExpr).

2. Because a terminator is seen, the below branch will be executed when visiting the 2nd stmt:

   llvm-project/clang/lib/CodeGen/CoverageMappingGen.cpp

   Lines 1375 to 1376 in e6c3289

   	if (LastStmt && HasTerminateStmt && !isa<AttributedStmt>(Child)) {
   	auto Gap = findGapAreaBetween(getEnd(LastStmt), getStart(Child));

3. However, the 2nd stmt doesn't have a valid source location and will fail some assertions in findGapAreaBetween().

---

Full diff: https://github.com/llvm/llvm-project/pull/89564.diff

1 Files Affected:

• (modified) clang/lib/CodeGen/CoverageMappingGen.cpp (+3-1)

diff --git a/clang/lib/CodeGen/CoverageMappingGen.cpp b/clang/lib/CodeGen/CoverageMappingGen.cpp
index 64c39c5de351c7..45296ff9cfb5e3 100644
--- a/clang/lib/CodeGen/CoverageMappingGen.cpp
+++ b/clang/lib/CodeGen/CoverageMappingGen.cpp
@@ -1370,7 +1370,9 @@ struct CounterCoverageMappingBuilder
         // If last statement contains terminate statements, add a gap area
         // between the two statements. Skipping attributed statements, because
         // they don't have valid start location.
-        if (LastStmt && HasTerminateStmt && !isa<AttributedStmt>(Child)) {
+        if (LastStmt && HasTerminateStmt && !isa<AttributedStmt>(Child) &&
+            !isa<ImplicitValueInitExpr>(Child) &&
+            !isa<ImplicitValueInitExpr>(LastStmt)) {
           auto Gap = findGapAreaBetween(getEnd(LastStmt), getStart(Child));
           if (Gap)
             fillGapAreaWithCount(Gap->getBegin(), Gap->getEnd(),

[ZequanWu]

There could be some other statements with invalid source locations (we have seen that before). I suggest validating both source locations inside findGapAreaBetween and returning std::nullopt if either of them is invalid.

Also need a test case. You can add the crashed example as a test case under clang/test/CoverageMapping.

[whentojump]

Thanks for your suggestion! @ZequanWu

Would you please take another look?

[whentojump]

Fwiw, I uncovered #86998 in the first place when I was compiling this file in Linux kernel: https://elixir.bootlin.com/linux/v6.8.1/source/fs/coredump.c#L545. I can confirm on my local side, with this patch, fs/coredump.o can be compiled and instrumented successfully.

I am going to squash merge this PR.

[whentojump]

/cherry-pick c1b6cca

[llvmbot]

/pull-request #90369