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    • Chris Lattner's avatar
      Fix a long standing deficiency in the X86 backend: we would · 5728bdd4
      Chris Lattner authored
      sometimes emit "zero" and "all one" vectors multiple times,
      for example:
      
      _test2:
      	pcmpeqd	%mm0, %mm0
      	movq	%mm0, _M1
      	pcmpeqd	%mm0, %mm0
      	movq	%mm0, _M2
      	ret
      
      instead of:
      
      _test2:
      	pcmpeqd	%mm0, %mm0
      	movq	%mm0, _M1
      	movq	%mm0, _M2
      	ret
      
      This patch fixes this by always arranging for zero/one vectors
      to be defined as v4i32 or v2i32 (SSE/MMX) instead of letting them be
      any random type.  This ensures they get trivially CSE'd on the dag.
      This fix is also important for LegalizeDAGTypes, as it gets unhappy
      when the x86 backend wants BUILD_VECTOR(i64 0) to be legal even when
      'i64' isn't legal.
      
      This patch makes the following changes:
      
      1) X86TargetLowering::LowerBUILD_VECTOR now lowers 0/1 vectors into
         their canonical types.
      2) The now-dead patterns are removed from the SSE/MMX .td files.
      3) All the patterns in the .td file that referred to immAllOnesV or
         immAllZerosV in the wrong form now use *_bc to match them with a
         bitcast wrapped around them.
      4) X86DAGToDAGISel::SelectScalarSSELoad is generalized to handle 
         bitcast'd zero vectors, which simplifies the code actually.
      5) getShuffleVectorZeroOrUndef is updated to generate a shuffle that
         is legal, instead of generating one that is illegal and expecting
         a later legalize pass to clean it up.
      6) isZeroShuffle is generalized to handle bitcast of zeros.
      7) several other minor tweaks.
      
      This patch is definite goodness, but has the potential to cause random
      code quality regressions.  Please be on the lookout for these and let 
      me know if they happen.
      
      llvm-svn: 44310
      5728bdd4
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