Stack overflow from `spvtools::opt::SSARewriter::GetReachingDef` recursion

[devshgraphicsprogramming]

Achieved on a similar test case to #6104

We're compiling this HLSL shader which we need to compile with -fcgl to get to the SPIR-V
https://godbolt.org/z/r75PE1xWM

The resulting SPIR-V attached

I don't know how to invoke the spv-opt properly on Godbolt with illegal SPIR-V, probably assembler complains before even seeing --legalize-hlsl
https://godbolt.org/z/fEMcoKTv3

Results in this callstack before crashing in DXC without the -fcgl flag inside of SPIR-V Opt.

 	msvcp140d.dll!00007ff8c692076e()	Unknown
 	msvcp140d.dll!00007ff8c691ea06()	Unknown
>	dxcompiler.dll!std::_Iterator_base12::_Adopt_locked(const std::_Container_base12 * _Parent) Line 1367	C++
 	dxcompiler.dll!std::_Iterator_base12::_Adopt(const std::_Container_base12 * _Parent) Line 1307	C++
 	dxcompiler.dll!std::_List_unchecked_const_iterator<std::_List_val<std::_List_simple_types<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>>>,std::_Iterator_base12>::_List_unchecked_const_iterator<std::_List_val<std::_List_simple_types<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>>>,std::_Iterator_base12>(std::_List_node<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>,void *> * _Pnode, const std::_List_val<std::_List_simple_types<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>>> * _Plist) Line 38	C++
 	dxcompiler.dll!std::_List_const_iterator<std::_List_val<std::_List_simple_types<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>>>>::_List_const_iterator<std::_List_val<std::_List_simple_types<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>>>>(std::_List_node<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>,void *> *)	C++
 	dxcompiler.dll!std::_List_iterator<std::_List_val<std::_List_simple_types<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>>>>::_List_iterator<std::_List_val<std::_List_simple_types<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>>>>(std::_List_node<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>,void *> *)	C++
 	dxcompiler.dll!std::list<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>,std::allocator<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>>>::_Make_iter(std::_List_node<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>,void *> * _Where) Line 1137	C++
 	dxcompiler.dll!std::_Hash<std::_Umap_traits<spvtools::opt::BasicBlock *,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>,std::_Uhash_compare<spvtools::opt::BasicBlock *,std::hash<spvtools::opt::BasicBlock *>,std::equal_to<spvtools::opt::BasicBlock *>>,std::allocator<std::pair<spvtools::opt::BasicBlock * const,std::unordered_map<unsigned int,unsigned int,std::hash<unsigned int>,std::equal_to<unsigned int>,std::allocator<std::pair<unsigned int const ,unsigned int>>>>>,0>>::find(spvtools::opt::BasicBlock * const & _Keyval) Line 1231	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetValueAtBlock(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 247	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 260	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
 	dxcompiler.dll!spvtools::opt::SSARewriter::GetReachingDef(unsigned int var_id, spvtools::opt::BasicBlock * bb) Line 268	C++
...
 	The maximum number of stack frames supported by Visual Studio has been exceeded.

Its also possible that the illegal SPIR-V emitted by DXC is causing infinite recursion / loops in the parsed SPIR-V, because the input HLSL is just a simple unit-test shader, so I doubt the chains are so deep to actually overflow the stack which is a few megs.

[devshgraphicsprogramming]

@s-perron @Madman10K can a fix similar to the one for #6104 be made?

CC: @Fletterio @kevyuu

[devshgraphicsprogramming]

@Przemog1 @keptsecret it affects your unit tests too if they get too long