[llvm-bugs] [Bug 43383] New: LLVM miscompiles trivial switch for AArch64

via llvm-bugs llvm-bugs at lists.llvm.org
Fri Sep 20 10:50:33 PDT 2019


            Bug ID: 43383
           Summary: LLVM miscompiles trivial switch for AArch64
           Product: new-bugs
           Version: 9.0
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: andrew at ziglang.org
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

I'm filing this on behalf of downstream issue:

Here's the reduced llvm-ir test case:

; Function Attrs: cold nobuiltin noreturn nounwind                              
define internal void @bar() unnamed_addr #1 {                                   

define i1 @foo(i1) unnamed_addr #0 {                                            
  switch i1 %0, label %BadValue [                                               
    i1 false, label %OkValue                                                    
    i1 true, label %OkValue                                                     

  call fastcc void @bar()                                                       

  ret i1 %0                                                                     

LLVM9 generates nonsensical code:

    mov w8, #1                                                                  
    mov w9, w0                                                                  
    and w9, w9, w8                                                              
    mov w10, #0                                                                 
    and w8, w10, w8 // w8 is turned into zero     
    cmp w9, w8 // Comparison against zero
    str w0, [sp, #12]                 
    b.ls    .LBB1_2 // The branch is _never_ taken

Please report to the LLVM devs, I have no bugzilla account.

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