The goal of this PR is to fix an issue when Module Analysis stage is not
able to complete processing of a really big LLVM source:
https://github.com/llvm/llvm-project/issues/76048.
There is an example of a bulky LLVM source:
https://github.com/KhronosGroup/SPIRV-LLVM-Translator/blob/main/test/SpecConstants/long-spec-const-composite.ll
Processing of this file with
`llc -mtriple=spirv64-unknown-unknown -O0 long-spec-const-composite.ll
-o long-spec-const-composite.spvt`
to produce SPIR-V output using LLVM SPIR-V backend takes too long, and
I've never been able to see it actually completes. After the patch from
this PR applied elapsed time for me is ~30 sec.
The fix changes underlying data structure to be `std::set` to trace
instructions with identical operands instead of the existing approach of
the `findSameInstrInMS()` function.
774b957786