[6.0] [loadable by address reg2mem] Implement missing throw instruction

Description: Fixes a missing case to large types reg2mem. Without adding
this case asserts compiler will complain and cause the compiler to
crash.

Risk: Low. This is the same code that we would have generated with an no-asserts
compiler where we fallback to a solution that loads and stores back to memory.

Scope: Fixes a compiler crasher in asserts toolchains.

Testing: Regression test added.

rdar://134914984
(cherry picked from commit eeaf962)

Author: aschwaighofer

lib/IRGen/LoadableByAddress.cpp

@@ -3861,6 +3861,10 @@ class RewriteUser : SILInstructionVisitor<RewriteUser> {
     userInstructionFallback(kp);
   }
 
+  void visitYieldInst(YieldInst *yield) { userInstructionFallback(yield); }
+
+  void visitThrowInst(ThrowInst *t) { userInstructionFallback(t); }
+
   void visitFixLifetimeInst(FixLifetimeInst *f) {
     auto addr = assignment.getAddressForValue(f->getOperand());
     auto builder = assignment.getBuilder(f->getIterator());

test/IRGen/loadable_by_address_reg2mem.sil

@@ -306,3 +306,16 @@ bb0(%0 : $*X):
   dealloc_stack %1 : $*Y
   return %13 : $()
 }
+
+// CHECK: sil @test14
+// CHECK:   [[VAL:%.*]] = load {{.*}} : $*X
+// CHECK:   throw [[VAL]]
+// CHECK: } // end sil function 'test14'
+sil @test14 : $@convention(thin) (@in X) -> @error X {
+bb0(%0 : $*X):
+  %1 = alloc_stack $X
+  copy_addr [take] %0 to [init] %1 : $*X
+  %3 = load %1 : $*X
+  dealloc_stack %1 : $*X
+  throw %3 : $X
+}