[Clang] Fix crash in coverage of if consteval.

[cor3ntin]

Summary

Clang crashes when encountering an if consteval statement.
This is the minimum fix not to crash.
The fix is consistent with the current behavior of if constexpr,
which does generate coverage data for the discarded branches.
This is of course not correct and a better solution is
needed for both if constexpr and if consteval.
See https://github.com/llvm/llvm-project/issues/54419.

Fixes #57377

[cor3ntin]

@aaron.ballman I did a minimal fix, both because It's unclear to me how coverage work and because I think we should try to land this is 15.
I hope that's okay.

[aaron.ballman]

Can you also add a release note?

clang/lib/CodeGen/CoverageMappingGen.cpp

1375

Spurious whitespace change.

1380–1382

Fighting our usual crusade against braces.

1406–1407

1. Pick a name which doesn't shadow
2. Spell out the type instead of using auto

[cor3ntin]

Release notes + style issues (There was no shadowing though)

[cor3ntin]

clang/lib/CodeGen/CoverageMappingGen.cpp

1406–1407

auto Gap... was preexisting, I changed both instances. Both variables are in their own non nested scopes though.

[cor3ntin]

Formatting

[aaron.ballman]

LGTM, thanks for the fix!

clang/lib/CodeGen/CoverageMappingGen.cpp

1406–1407

Yeah, I somehow missed these were in different scopes!

clang/docs/ReleaseNotes.rst

- Fix `#57008 <https://github.com/llvm/llvm-project/issues/57008>`_ - Builtin
   number of arguments cause an assertion fault.
 - Fix multi-level pack expansion of undeclared function parameters.
   This fixes `Issue 56094 <https://github.com/llvm/llvm-project/issues/56094>`_.
 - Fix `#57151 <https://github.com/llvm/llvm-project/issues/57151>`_.
   ``-Wcomma`` is emitted for void returning functions.
 - ``-Wtautological-compare`` missed warnings for tautological comparisons
   involving a negative integer literal. This fixes
   `Issue 42918 <https://github.com/llvm/llvm-project/issues/42918>`_.
+- Fix a crash when generating code coverage information for an
+  ``if consteval`` statement. This fixes
+  `Issue 57377 <https://github.com/llvm/llvm-project/issues/57377>`_.
+
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 - Clang will now correctly diagnose as ill-formed a constant expression where an
   enum without a fixed underlying type is set to a value outside the range of
   the enumeration's values. Due to the extended period of time this bug was
   present in major C++ implementations (including Clang), this error has the
   ability to be downgraded into a warning (via: -Wno-error=enum-constexpr-conversion)

clang/lib/CodeGen/CoverageMappingGen.cpp

if (const auto *CS = dyn_cast<CaseStmt>(S)) {
       if (const Expr *RHS = CS->getRHS())
         Visit(RHS);
     }
     Visit(S->getSubStmt());
   }
 
   void VisitIfStmt(const IfStmt *S) {
     extendRegion(S);
     if (S->getInit())
       Visit(S->getInit());
 
     // Extend into the condition before we propagate through it below - this is
     // needed to handle macros that generate the "if" but not the condition.
+    if (!S->isConsteval())
       extendRegion(S->getCond());
 
     Counter ParentCount = getRegion().getCounter();
     Counter ThenCount = getRegionCounter(S);
 
+    if (!S->isConsteval()) {
       // Emitting a counter for the condition makes it easier to interpret the
       // counter for the body when looking at the coverage.
       propagateCounts(ParentCount, S->getCond());
 
       // The 'then' count applies to the area immediately after the condition.
-    auto Gap = findGapAreaBetween(S->getRParenLoc(), getStart(S->getThen()));
+      Optional<SourceRange> Gap =
+          findGapAreaBetween(S->getRParenLoc(), getStart(S->getThen()));
       if (Gap)
         fillGapAreaWithCount(Gap->getBegin(), Gap->getEnd(), ThenCount);
+    }
 
     extendRegion(S->getThen());
     Counter OutCount = propagateCounts(ThenCount, S->getThen());
 
     Counter ElseCount = subtractCounters(ParentCount, ThenCount);
     if (const Stmt *Else = S->getElse()) {
       bool ThenHasTerminateStmt = HasTerminateStmt;
       HasTerminateStmt = false;
-
       // The 'else' count applies to the area immediately after the 'then'.
-      Gap = findGapAreaBetween(getEnd(S->getThen()), getStart(Else));
+      Optional<SourceRange> Gap =
+          findGapAreaBetween(getEnd(S->getThen()), getStart(Else));
       if (Gap)
         fillGapAreaWithCount(Gap->getBegin(), Gap->getEnd(), ElseCount);
       extendRegion(Else);
       OutCount = addCounters(OutCount, propagateCounts(ElseCount, Else));
 
       if (ThenHasTerminateStmt)
         HasTerminateStmt = true;
     } else
       OutCount = addCounters(OutCount, ElseCount);
 
     if (OutCount != ParentCount) {
       pushRegion(OutCount);
       GapRegionCounter = OutCount;
     }
 
+    if (!S->isConsteval()) {
       // Create Branch Region around condition.
       createBranchRegion(S->getCond(), ThenCount,
                          subtractCounters(ParentCount, ThenCount));
     }
+  }
 
   void VisitCXXTryStmt(const CXXTryStmt *S) {
     extendRegion(S);
     // Handle macros that generate the "try" but not the rest.
     extendRegion(S->getTryBlock());
 
     Counter ParentCount = getRegion().getCounter();
     propagateCounts(ParentCount, S->getTryBlock());

clang/test/CoverageMapping/if.cpp

-// RUN: %clang_cc1 -mllvm -emptyline-comment-coverage=false -fprofile-instrument=clang -fcoverage-mapping -dump-coverage-mapping -emit-llvm-only -std=c++1z -triple %itanium_abi_triple -main-file-name if.cpp %s | FileCheck %s
+// RUN: %clang_cc1 -mllvm -emptyline-comment-coverage=false -fprofile-instrument=clang -fcoverage-mapping -dump-coverage-mapping -emit-llvm-only -std=c++2b -triple %itanium_abi_triple -main-file-name if.cpp %s | FileCheck %s
 
 int nop() { return 0; }
 
 // CHECK-LABEL: _Z3foov:
                                 // CHECK-NEXT: [[@LINE+3]]:12 -> [[@LINE+8]]:2 = #0
                                 // CHECK-NEXT: [[@LINE+3]]:15 -> [[@LINE+3]]:19 = #0
                                 // CHECK-NEXT: Branch,File 0, [[@LINE+2]]:15 -> [[@LINE+2]]:19 = 0, 0
 void foo() {                    // CHECK-NEXT: Gap,File 0, [[@LINE+1]]:21 -> [[@LINE+1]]:22 = #2
   if (int j = true ? nop()      // CHECK-NEXT: [[@LINE]]:22 -> [[@LINE]]:27 = #2
                    : nop();     // CHECK-NEXT: [[@LINE]]:22 -> [[@LINE]]:27 = (#0 - #2)
       j)                        // CHECK-NEXT: [[@LINE]]:7 -> [[@LINE]]:8 = #0
     ++j;                        // CHECK-NEXT: Branch,File 0, [[@LINE-1]]:7 -> [[@LINE-1]]:8 = #1, (#0 - #1)
 }                               // CHECK-NEXT: [[@LINE-2]]:9 -> [[@LINE-1]]:5 = #1
                                 // CHECK-NEXT: [[@LINE-2]]:5 -> [[@LINE-2]]:8 = #1
+
+// FIXME: Do not generate coverage for discarded branches in if consteval and if constexpr statements
+constexpr int check_consteval(int i) {
+    if consteval {
+      i++;
+    }
+    if !consteval {
+      i++;
+    }
+    if consteval {
+        return 42;
+    } else {
+        return i;
+    }
+}
+
 // CHECK-LABEL: main:
 int main() {                    // CHECK: File 0, [[@LINE]]:12 -> {{[0-9]+}}:2 = #0
   int i = 0;
                                 // CHECK-NEXT: File 0, [[@LINE+3]]:6 -> [[@LINE+3]]:12 = #0
                                 // CHECK-NEXT: Branch,File 0, [[@LINE+2]]:6 -> [[@LINE+2]]:12 = #1, (#0 - #1)
                                 // CHECK-NEXT: Gap,File 0, [[@LINE+1]]:13 -> [[@LINE+1]]:14 = #1
   if(i == 0) i = 1;             // CHECK-NEXT: File 0, [[@LINE]]:14 -> [[@LINE]]:19 = #1
 
i = i == 0?                   // CHECK-NEXT: Gap,File 0, [[@LINE]]:14 -> [[@LINE+1]]:9 = #5
         i + 1 :                 // CHECK-NEXT: File 0, [[@LINE]]:9 -> [[@LINE]]:14 = #5
         i + 2;                  // CHECK-NEXT: File 0, [[@LINE]]:9 -> [[@LINE]]:14 = (#0 - #5)
 
                                 // CHECK-NEXT: File 0, [[@LINE+3]]:7 -> [[@LINE+3]]:13 = #0
                                 // CHECK-NEXT: Branch,File 0, [[@LINE+2]]:7 -> [[@LINE+2]]:13 = #6, (#0 - #6)
                                 // CHECK-NEXT: File 0, [[@LINE+1]]:14 -> [[@LINE+1]]:20 = #6
   i = i == 0?i + 12:i + 10;     // CHECK-NEXT: File 0, [[@LINE]]:21 -> [[@LINE]]:27 = (#0 - #6)
 
+  // GH-57377
+  constexpr int c_i = check_consteval(0);
+  check_consteval(i);
+
   return 0;
 }
 
 #define FOO true
 
 // CHECK-LABEL: _Z7ternaryv:
 void ternary() {
   true ? FOO : FOO; // CHECK-NOT: Gap,{{.*}}, [[@LINE]]:8 ->
 }