[ubsan][NFCI] Use SanitizerOrdinal instead of SanitizerMask for EmitCheck (exactly one sanitizer is required) (#122511)

The `Checked` parameter of `CodeGenFunction::EmitCheck` is of type
`ArrayRef<std::pair<llvm::Value *, SanitizerMask>>`, which is overly
generalized: SanitizerMask can denote that zero or more sanitizers are
enabled, but `EmitCheck` requires that exactly one sanitizer is
specified in the SanitizerMask (e.g.,
`SanitizeTrap.has(Checked[i].second)` enforces that).

This patch replaces SanitizerMask with SanitizerOrdinal in the `Checked`
parameter of `EmitCheck` and code that transitively relies on it. This
should not affect the behavior of UBSan, but it has the advantages that:
- the code is clearer: it avoids ambiguity in EmitCheck about what to do
if multiple bits are set
- specifying the wrong number of sanitizers in `Checked[i].second` will
be detected as a compile-time error, rather than a runtime assertion
failure

Suggested by Vitaly in https://github.com/llvm/llvm-project/pull/122392
as an alternative to adding an explicit runtime assertion that the
SanitizerMask contains exactly one sanitizer.

1 files changed, 5 insertions, 4 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 27ec68b..d6f3716 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -1600,7 +1600,7 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
     if (SanOpts.has(SanitizerKind::Return)) {
       SanitizerScope SanScope(this);
       llvm::Value *IsFalse = Builder.getFalse();
-      EmitCheck(std::make_pair(IsFalse, SanitizerKind::Return),
+      EmitCheck(std::make_pair(IsFalse, SanitizerKind::SO_Return),
                 SanitizerHandler::MissingReturn,
                 EmitCheckSourceLocation(FD->getLocation()), {});
     } else if (ShouldEmitUnreachable) {
@@ -2484,8 +2484,9 @@ void CodeGenFunction::EmitVariablyModifiedType(QualType type) {
             llvm::Constant *StaticArgs[] = {
                 EmitCheckSourceLocation(sizeExpr->getBeginLoc()),
                 EmitCheckTypeDescriptor(SEType)};
-            EmitCheck(std::make_pair(CheckCondition, SanitizerKind::VLABound),
-                      SanitizerHandler::VLABoundNotPositive, StaticArgs, size);
+            EmitCheck(
+                std::make_pair(CheckCondition, SanitizerKind::SO_VLABound),
+                SanitizerHandler::VLABoundNotPositive, StaticArgs, size);
           }
 
           // Always zexting here would be wrong if it weren't
@@ -3139,7 +3140,7 @@ void CodeGenFunction::emitAlignmentAssumptionCheck(
     llvm::Value *DynamicData[] = {EmitCheckValue(Ptr),
                                   EmitCheckValue(Alignment),
                                   EmitCheckValue(OffsetValue)};
-    EmitCheck({std::make_pair(TheCheck, SanitizerKind::Alignment)},
+    EmitCheck({std::make_pair(TheCheck, SanitizerKind::SO_Alignment)},
               SanitizerHandler::AlignmentAssumption, StaticData, DynamicData);
   }