48 lines
1.8 KiB
Text
48 lines
1.8 KiB
Text
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IRgen optimization opportunities.
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//===---------------------------------------------------------------------===//
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The common pattern of
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--
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short x; // or char, etc
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(x == 10)
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--
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generates an zext/sext of x which can easily be avoided.
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//===---------------------------------------------------------------------===//
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Bitfields accesses can be shifted to simplify masking and sign
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extension. For example, if the bitfield width is 8 and it is
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appropriately aligned then is is a lot shorter to just load the char
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directly.
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//===---------------------------------------------------------------------===//
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It may be worth avoiding creation of alloca's for formal arguments
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for the common situation where the argument is never written to or has
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its address taken. The idea would be to begin generating code by using
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the argument directly and if its address is taken or it is stored to
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then generate the alloca and patch up the existing code.
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In theory, the same optimization could be a win for block local
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variables as long as the declaration dominates all statements in the
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block.
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NOTE: The main case we care about this for is for -O0 -g compile time
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performance, and in that scenario we will need to emit the alloca
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anyway currently to emit proper debug info. So this is blocked by
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being able to emit debug information which refers to an LLVM
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temporary, not an alloca.
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//===---------------------------------------------------------------------===//
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We should try and avoid generating basic blocks which only contain
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jumps. At -O0, this penalizes us all the way from IRgen (malloc &
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instruction overhead), all the way down through code generation and
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assembly time.
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On 176.gcc:expr.ll, it looks like over 12% of basic blocks are just
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direct branches!
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//===---------------------------------------------------------------------===//
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