[ubsan] Add -fsanitize-merge (and -fno-sanitize-merge) (#120464)

'-mllvm -ubsan-unique-traps'
(https://github.com/llvm/llvm-project/pull/65972) applies to all UBSan
checks. This patch introduces -fsanitize-merge (defaults to on,
maintaining the status quo behavior) and -fno-sanitize-merge (equivalent
to '-mllvm -ubsan-unique-traps'), with the option to selectively
applying non-merged handlers to a subset of UBSan checks (e.g.,
-fno-sanitize-merge=bool,enum).

N.B. we do not use "trap" in the argument name since
https://github.com/llvm/llvm-project/pull/119302 has generalized
-ubsan-unique-traps to work for non-trap modes (min-rt and regular rt).

This patch does not remove the -ubsan-unique-traps flag; that will
override -f(no-)sanitize-merge.

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 298fafc..348c56c 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1792,6 +1792,10 @@ void CompilerInvocationBase::GenerateCodeGenArgs(const CodeGenOptions &Opts,
   for (StringRef Sanitizer : serializeSanitizerKinds(Opts.SanitizeTrap))
     GenerateArg(Consumer, OPT_fsanitize_trap_EQ, Sanitizer);
 
+  for (StringRef Sanitizer :
+       serializeSanitizerKinds(Opts.SanitizeMergeHandlers))
+    GenerateArg(Consumer, OPT_fsanitize_merge_handlers_EQ, Sanitizer);
+
   if (!Opts.EmitVersionIdentMetadata)
     GenerateArg(Consumer, OPT_Qn);
 
@@ -2269,6 +2273,9 @@ bool CompilerInvocation::ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args,
   parseSanitizerKinds("-fsanitize-trap=",
                       Args.getAllArgValues(OPT_fsanitize_trap_EQ), Diags,
                       Opts.SanitizeTrap);
+  parseSanitizerKinds("-fsanitize-merge=",
+                      Args.getAllArgValues(OPT_fsanitize_merge_handlers_EQ),
+                      Diags, Opts.SanitizeMergeHandlers);
 
   Opts.EmitVersionIdentMetadata = Args.hasFlag(OPT_Qy, OPT_Qn, true);