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1feb97a12b
This algorithm (explained more in the source code) takes into account global redundancies by building a "pair map" to find common subexprs. The primary motivation of this is to handle situations like foo = (a * b) * c bar = (a * d) * c where we currently don't identify that "a * c" is redundant. Accordingly, it prioritizes the emission of a * c so that CSE can remove the redundant calculation later. Does not change the actual reassociation algorithm -- only the order in which the reassociated operand chain is reconstructed. Gives ~1.5% floating point math instruction count reduction on a large offline suite of graphics shaders. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@320515 91177308-0d34-0410-b5e6-96231b3b80d8