[clang] [llvm] [SystemZ] Add support for __builtin_setjmp and __builtin_longjmp (PR #116642)

[Ulrich Weigand via cfe-commits]

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@@ -4619,6 +4619,12 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
     // Buffer is a void**.
     Address Buf = EmitPointerWithAlignment(E->getArg(0));
 
+    if (getTarget().getTriple().getArch() == llvm::Triple::systemz) {
+      // Call LLVM's EH setjmp, which is lightweight.
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uweigand wrote:

I see.  It seems back in the day the `eh.sjlj.setjmp` intrinsic was used by both the front-end to implement `__builtin_setjmp` and by the middle-end (SjLjEHPrepare.cpp) for exception handling.  Since these two users apparently require somewhat different information in the buffer, filling this in was left to the user.

However, these days those two users actually emit two different intrinsics.  The middle-end now uses `eh.sjlj.setup.dispatch` (which is apparently only intended for internal usage; it's not documented at all), while only the front-end continues to use `eh.sjlj.setjmp`.  See http://reviews.llvm.org/D9313.

I still think the most straightfoward way would be to have `eh.sjlj.setjmp` just be completely implemented in the back end, and simply do exactly what is needed to implement `__builtin_setjmp` on the platform, just like is done with longjmp.  This could be done for all targets (probably the cleanest solution, but would require updating the existing targets and might introduce incompatibilities with existing bytecode on those targets), or just for selected targets (I guess this would then need to be documented?  And should it be a positive or negative list of targets?).


https://github.com/llvm/llvm-project/pull/116642