swift234

Optimize how most derived type is computed in the new projection path Instead of walking the
entire projection path to find the most derived type, we cache it and invalidate when the projectionpath is
append'ed to.

stdlib -O

=== Before ===
Running Time        Self (ms)               Symbol Name
25741.0ms   37.3%   0.0                 swift::runSILOptimizationPasses(swift::SILModule&)
25523.0ms   37.0%   0.0                  swift::SILPassManager::runOneIteration()
20654.0ms   29.9%   36.0                  swift::SILPassManager::runFunctionPasses(llvm::ArrayRef<swift::SILFunctionTransform*>)
19663.0ms   28.5%   87.0                   swift::SILPassManager::runPassesOnFunction(llvm::ArrayRef<swift::SILFunctionTransform*>, swift::SILFunction*)
3279.0ms    4.7%    5.0                     (anonymous namespace)::SimplifyCFGPass::run()
3205.0ms    4.6%    11.0                    (anonymous namespace)::ARCSequenceOpts::run()
2550.0ms    3.7%    7.0                     (anonymous namespace)::SILCombine::run()
2177.0ms    3.1%    42.0                    (anonymous namespace)::RedundantLoadElimination::run()
2151.0ms    3.1%    115.0                   (anonymous namespace)::SILCSE::run()
1255.0ms    1.8%    18.0                    (anonymous namespace)::GenericSpecializer::run()
1080.0ms    1.5%    49.0                    (anonymous namespace)::DeadStoreElimination::run()
926.0ms    1.3%     189.0                   (anonymous namespace)::DCE::run()
488.0ms    0.7%     3.0                     (anonymous namespace)::SILCodeMotion::run()

=== After ===
Running Time        Self (ms)               Symbol Name
24065.0ms   36.8%   0.0                 swift::runSILOptimizationPasses(swift::SILModule&)
23865.0ms   36.5%   0.0                  swift::SILPassManager::runOneIteration()
19245.0ms   29.4%   42.0                  swift::SILPassManager::runFunctionPasses(llvm::ArrayRef<swift::SILFunctionTransform*>)
18273.0ms   27.9%   65.0                   swift::SILPassManager::runPassesOnFunction(llvm::ArrayRef<swift::SILFunctionTransform*>, swift::SILFunction*)
3096.0ms    4.7%    10.0                    (anonymous namespace)::ARCSequenceOpts::run()
3081.0ms    4.7%    9.0                     (anonymous namespace)::SimplifyCFGPass::run()
2381.0ms    3.6%    8.0                     (anonymous namespace)::SILCombine::run()
1990.0ms    3.0%    128.0                   (anonymous namespace)::SILCSE::run()
1828.0ms    2.8%    65.0                    (anonymous namespace)::RedundantLoadElimination::run()
1200.0ms    1.8%    10.0                    (anonymous namespace)::GenericSpecializer::run()
918.0ms    1.4%     58.0                    (anonymous namespace)::DeadStoreElimination::run()
867.0ms    1.3%     140.0                   (anonymous namespace)::DCE::run()
479.0ms    0.7%     11.0                    (anonymous namespace)::SILCodeMotion::run()
294.0ms    0.4%     1.0                     (anonymous namespace)::ConstantPropagation::run()