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9c22aeb0b2
1) For 8-bit registers try to use first the ones that are parts of the same register (AL then AH). This way we only alias 2 16/32-bit registers after allocating 4 8-bit variables. 2) Move EBX as the last register to allocate. This will cause less spills to happen since we will have 8-bit registers available up to register excaustion (assuming we use the allocation order). It would be nice if we could push all of the 8-bit aliased registers towards the end but we much prefer to keep callee saved register to the end to avoid saving them on entry and exit of the function. For example this gives a slight reduction of spills with linear scan on 164.gzip. Before: 11221 asm-printer - Number of machine instrs printed 975 spiller - Number of loads added 675 spiller - Number of stores added 398 spiller - Number of register spills After: 11182 asm-printer - Number of machine instrs printed 952 spiller - Number of loads added 652 spiller - Number of stores added 386 spiller - Number of register spills git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11996 91177308-0d34-0410-b5e6-96231b3b80d8