[LLVMdev] ValueMapper question: no type mapping for GlobalValue?

[Michael Muller]

=?ISO-8859-1?Q?Rafael_=C1vila_de_Esp=EDndola?= wrote:
> On 11/01/12 07:50 AM, Michael Muller wrote:
> > 
> > Hi all, I was looking at the ValueMapper code this morning and I notice that
> > it doesn't do type mapping for GlobalValues.  Is this correct?
> > 
> > I ask because I am seeing a case where I'm failing type assertions from
> > ModuleLinker::linkGlobalInits() when an array initializer references an
> > external global.  It looks like the external global is being mapped directly
> > and this causes an element type check to fail in ConstantArray::get().
> > Curiously, this only happens when that external global is also referenced from
> > within a function in the same module.
> > 
> 
> Do you have a testcase?
> 
> I tried to reproduce this with
> 
> -----------
> a = global i64 42, align 8
> -----------
> 
> and
> 
> ----------
> @a = external global i32
> @b = constant [1 x i32*] [i32* @a], align 8
> 
> define i32 @f() nounwind uwtable readonly optsize {
> entry:
>   %0 = load i32* @a, align 4
>   ret i32 %0
> }
> ----------
> 
> but llvm-link correctly produced
> 
> 
> @b = constant [1 x i32*] [i32* bitcast (i64* @a to i32*)], align 8
> @a = global i64 42, align 8
> 
> define i32 @f() nounwind uwtable readonly optsize {
> entry:
>   %0 = load i32* bitcast (i64* @a to i32*), align 4
>   ret i32 %0
> }

I can reproduce this consistently, but only under an extremely large pile of
code :-)  I haven't tried to strip it down to minimal a test case yet, but I
will.  One salient difference with the code you've provided is that in my
code, @a is a struct type.  However, changing the example to use a minimal
structure doesn't trigger the assertion failure.

But I'm still curious: why doesn't the value mapper do type mapping on global
variables?

> 
> 
> Cheers,
> Rafael
> 
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