[LLVMbugs] [Bug 22476] New: missed store sinking opportunity?

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Thu Feb 5 04:59:25 PST 2015


            Bug ID: 22476
           Summary: missed store sinking opportunity?
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: junyer at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 13810
  --> http://llvm.org/bugs/attachment.cgi?id=13810&action=edit
function that returns true if a string contains 'a', 'b' or 'c'

It seems as though the `movb $1, %al' could be sunk from BB#3 to BB#4. :)

$ llc abc.ll 
$ cat abc.s
    .file    "abc.ll"
    .globl    F
    .align    16, 0x90
    .type    F, at function
F:                                      # @F
# BB#0:                                 # %entry
    .align    16, 0x90
.LBB0_1:                                # =>This Inner Loop Header: Depth=1
    testl    %esi, %esi
    je    .LBB0_2
# BB#3:                                 #   in Loop: Header=BB0_1 Depth=1
    movb    (%rdi), %al
    incq    %rdi
    decl    %esi
    addb    $-97, %al
    movzbl    %al, %ecx
    movb    $1, %al
    cmpl    $3, %ecx
    jae    .LBB0_1
# BB#4:                                 # %return_true
                                        # kill: AL<def> AL<kill> EAX<kill>
    xorl    %eax, %eax
                                        # kill: AL<def> AL<kill> EAX<kill>
    .size    F, .Ltmp0-F

    .section    ".note.GNU-stack","", at progbits

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