[llvm-dev] Dependence Analysis bug or undefined behavior?

[De Azevedo Piovezan, Felipe via llvm-dev]

Hi,

Does this kind of IR have "undefined behavior"  under LLVM semantics or is it acceptable?

(TLDR: a store of i64 at offset n, followed by a load of i32 at offset n+1.)

define void @foo(i32* %A, i64 %n) {
entry:
  %arrayidx = getelementptr inbounds i32, i32* %A, i64 %n
  %arrayidx_cast = bitcast i32* %arrayidx to i64*
  store i64 0, i64* %arrayidx_cast, align 4
  %add1 = add i64 %n, 1
  %arrayidx2 = getelementptr inbounds i32, i32* %A, i64 %add1
  %0 = load i32, i32* %arrayidx2, align 4
  ret void
}

The result of Dependence Analysis is:

opt -analyze -da BitCasts.ll
Printing analysis 'Dependence Analysis' for function 'z0':
da analyze - none!          <<< this is between the store and itself, ok to be "none".
da analyze - none!          <<< this is between the store and the load!!!
da analyze - none!          <<< this is between the load and itself, ok to be "none".

Is dependence analysis right or wrong? This IR likely comes from some C++ code doing funny things with unions...

Thanks!

--
Felipe de Azevedo Piovezan

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