[Clang] Add -fwrapv-pointer flag (#122486)

GCC supports three flags related to overflow behavior:
 * `-fwrapv`: Makes signed integer overflow well-defined.
 * `-fwrapv-pointer`: Makes pointer overflow well-defined.
* `-fno-strict-overflow`: Implies `-fwrapv -fwrapv-pointer`, making both
signed integer overflow and pointer overflow well-defined.

Clang currently only supports `-fno-strict-overflow` and `-fwrapv`, but
not `-fwrapv-pointer`.

This PR proposes to introduce `-fwrapv-pointer` and adjust the semantics
of `-fwrapv` to match GCC.

This allows signed integer overflow and pointer overflow to be
controlled independently, while `-fno-strict-overflow` still exists to
control both at the same time (and that option is consistent across GCC
and Clang).

1 files changed, 4 insertions, 0 deletions

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 3bf124e..44dd699 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -3721,6 +3721,8 @@ void CompilerInvocationBase::GenerateLangArgs(const LangOptions &Opts,
   } else if (Opts.SignedOverflowBehavior == LangOptions::SOB_Defined) {
     GenerateArg(Consumer, OPT_fwrapv);
   }
+  if (Opts.PointerOverflowDefined)
+    GenerateArg(Consumer, OPT_fwrapv_pointer);
 
   if (Opts.MSCompatibilityVersion != 0) {
     unsigned Major = Opts.MSCompatibilityVersion / 10000000;
@@ -4138,6 +4140,8 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
   }
   else if (Args.hasArg(OPT_fwrapv))
     Opts.setSignedOverflowBehavior(LangOptions::SOB_Defined);
+  if (Args.hasArg(OPT_fwrapv_pointer))
+    Opts.PointerOverflowDefined = true;
 
   Opts.MSCompatibilityVersion = 0;
   if (const Arg *A = Args.getLastArg(OPT_fms_compatibility_version)) {