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

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43383

            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:
https://github.com/ziglang/zig/issues/3271

Here's the reduced llvm-ir test case:

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

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

BadValue:                                                                       
  call fastcc void @bar()                                                       
  unreachable                                                                   

OkValue:                                                                        
  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.

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20190920/c9de0872/attachment.html>