Zig: LLVM miscompiles trivial switch for AArch64

[LemonBoy]

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.

[andrewrk]

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

[andrewrk]

Looks like it's going to be a release blocker for 9.0.1 :+1:

[andrewrk]

comment 7

I've committed a fix in r372675. Please check it fixes your issue on the latest trunk build.

[LemonBoy]

I've committed a fix in r372675. Please check it fixes your issue on the latest trunk build.

The fix is working as intended, the tests are now passing.

[andrewrk]

The upstream fix is in the 9.0.1 release branch. I'll close this issue when LLVM 9.0.1 is released.

[XVilka]

It was released by the way: https://github.com/llvm/llvm-project/releases/tag/llvmorg-9.0.1

[andrewrk]

Fixed with the merge of llvm10 branch: 93c7fa105f9cc4dbb36192469ecff47102d955d6