Don't create Register decref-info entries

They might be ok if we allowed allocating callee-save registers, but
since we don't, they mean we are asking the unwinder to restore a
clobbered register.

This was happening in some places where we didn't call setupCall()
before calling a function.  This was previously ok since those cases would
always throw an exception and nothing would want the values of the
then-clobbered registers.

src/asm_writing/rewriter.cpp

@@ -1219,7 +1219,8 @@ std::vector<Location> Rewriter::getDecrefLocations() {
                 assert(indirectFor(l).offset % 8 == 0);
                 decref_infos.emplace_back(Location::Stack, indirectFor(l).offset / 8);
             } else if (l.type == Location::Register) {
-                decref_infos.emplace_back(l);
+                // CSRs shouldn't be getting allocated, and we should only be calling this at a callsite:
+                RELEASE_ASSERT(0, "we shouldn't be trying to decref anything in a register");
             } else
                 RELEASE_ASSERT(0, "not implemented");
         }
@@ -1864,6 +1865,7 @@ void Rewriter::_checkAndThrowCAPIException(RewriterVar* r, int64_t exc_val) {
     else
         assembler->cmp(var_reg, assembler::Immediate(exc_val));
 
+    _setupCall(false, RewriterVar::SmallVector(), RewriterVar::SmallVector());
     {
         assembler::ForwardJump jnz(*assembler, assembler::COND_NOT_ZERO);
         assembler->mov(assembler::Immediate((void*)throwCAPIException), assembler::R11);

src/codegen/baseline_jit.cpp

@@ -998,6 +998,7 @@ void JitFragmentWriter::_emitGetLocal(RewriterVar* val_var, const char* name) {
     assembler::Register var_reg = val_var->getInReg();
     assembler->test(var_reg, var_reg);
 
+    _setupCall(false, RewriterVar::SmallVector(), RewriterVar::SmallVector());
     {
         assembler::ForwardJump jnz(*assembler, assembler::COND_NOT_ZERO);
         assembler->mov(assembler::Immediate((uint64_t)name), assembler::RDI);

src/codegen/unwinding.cpp

@@ -522,6 +522,12 @@ void executeDecrefs(unw_cursor_t* cursor) {
         if (l.type == Location::Stack) {
             unw_word_t sp = get_cursor_sp(cursor);
             b = ((Box**)sp)[l.stack_offset];
+        } else if (l.type == Location::Register) {
+            RELEASE_ASSERT(0, "untested");
+            // This branch should never get hit since we shouldn't generate Register locations,
+            // since we don't allow allocating callee-save registers.
+            // If we did, this code might be right:
+            // b = (Box*)get_cursor_reg(cursor, l.regnum);
         } else {
             RELEASE_ASSERT(0, "not implemented");
         }