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  1. Jan 30, 2011
    • Benjamin Kramer's avatar
      Teach DAGCombine to fold fold (sra (trunc (sr x, c1)), c2) -> (trunc (sra x,... · 946e1522
      Benjamin Kramer authored
      Teach DAGCombine to fold fold (sra (trunc (sr x, c1)), c2) -> (trunc (sra x, c1+c2) when c1 equals the amount of bits that are truncated off.
      
      This happens all the time when a smul is promoted to a larger type.
      
      On x86-64 we now compile "int test(int x) { return x/10; }" into
        movslq  %edi, %rax
        imulq $1717986919, %rax, %rax
        movq  %rax, %rcx
        shrq  $63, %rcx
        sarq  $34, %rax <- used to be "shrq $32, %rax; sarl $2, %eax"
        addl  %ecx, %eax
      
      This fires 96 times in gcc.c on x86-64.
      
      llvm-svn: 124559
      946e1522
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