Common subexpression elimination for vasm#6843
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This diff adds a local common subexpression elimination vasm pass. It has basic block scope and works as described below: * searches for binary expressions inside a BB and saves them into a list * an instruction is considered to be a binary expression if it uses two operands and defines at least one * if an expression is already in the saved expression list, it's replaced by a "nop" instruction * all uses of registers which are defined by a redundant expression are replaced with registers defined by the matching expression (i.e. the expression found in the list) * if a register used by a saved expression is redefined by another instruction, the binary expression is removed from the list. This can only happen for physical registers, which are not in SSA form * SF registers are also considered non-SSA, since vasm-xls does not support overlapping liveness intervals for them.
First simplifier is used to remove redundant fallbackcc instructions from a basic block. The second one transforms a "jcc" into an unconditional "jmp" when a fallbackcc with the same condition and same SF is present in the same basic block. Example: cmpbim 0, [%rbp - 0x8] => %132 fallbackcc NE, (id 0x181f)@7, 1, %132, {%rbp, %r12} cmpbim 0, [%rbp - 0x8] => %133 jcc NE, %133, B5, else B12 After vasm-cse: cmpbim 0, [%rbp - 0x8] => %132 fallbackcc NE, (id 0x181f)@7, 1, %132, {%rbp, %r12} jcc NE, %132, B5, else B12 After vasm-simplify: cmpbim 0, [%rbp - 0x8] => %132 fallbackcc NE, (id 0x181f)@7, 1, %132, {%rbp, %r12} jmp B12
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