[ubsan] Assert that each check only has one SanitizerKind

[thurstond]

The Checked parameter of CodeGenFunction::EmitCheck is of type ArrayRef<std::pair<llvm::Value *, SanitizerMask>>. In the general case, SanitizerMask is used to denote that zero or more sanitizers are enabled, but I believe that EmitCheck assumes there is exactly one sanitizer enabled per SanitizerMask (e.g., SanitizeTrap.has(Checked[i].second) is called, whereby .has checks that there is only one sanitizer enabled). This patch adds an assertion for this invariant.

This is not intended to change the functionality of UBSan, but will make it easier for maintainers to reason about and extend the EmitCheck function.

[llvmbot]

@llvm/pr-subscribers-clang-codegen

@llvm/pr-subscribers-clang

Author: Thurston Dang (thurstond)

Changes

The Checked parameter of CodeGenFunction::EmitCheck is of type ArrayRef<std::pair<llvm::Value *, SanitizerMask>>. In the general case, SanitizerMask can denote that zero or more sanitizers are enabled, but I believe (from tests and inspecting the code) that EmitCheck assumes exactly one sanitizer enabled per SanitizerMask. This patch adds an assertion for this invariant.

This is not intended to change the functionality of UBSan, but will make it easier for maintainers to reason about and extend the EmitCheck function.

---

Full diff: https://github.com/llvm/llvm-project/pull/122392.diff

1 Files Affected:

• (modified) clang/lib/CodeGen/CGExpr.cpp (+2)

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 1bad7a722da07a..792fe05025e393 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -3603,6 +3603,8 @@ void CodeGenFunction::EmitCheck(
   llvm::Value *TrapCond = nullptr;
   bool NoMerge = false;
   for (int i = 0, n = Checked.size(); i < n; ++i) {
+    assert(Checked[i].second.isPowerOf2());
+
     llvm::Value *Check = Checked[i].first;
     // -fsanitize-trap= overrides -fsanitize-recover=.
     llvm::Value *&Cond =

[vitalybuka]

Maybe instead switch SanitizerMask -> SanitizerOrdinal?