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David Majnemer
80a961a80c
32-bit x86 Windows targets use a linked-list of nodes allocated on the stack, referenced to via thread-local storage. The personality routine interprets one of the fields in the node as a 'state number' which indicates where the personality routine should transfer control. State transitions are possible only before call-sites which may throw exceptions. Our previous scheme had us update the state number before all call-sites which may throw. Instead, we can try to minimize the number of times we need to store by reasoning about the nearest store which dominates the current call-site. If the last store agrees with the current call-site, then we know that the state-update is redundant and can be elided. This is largely straightforward: an RPO walk of the blocks allows us to correctly forward propagate the information when the function is a DAG. Currently, loops are not handled optimally and may trigger superfluous state stores. Differential Revision: http://reviews.llvm.org/D16763 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@261122 91177308-0d34-0410-b5e6-96231b3b80d8