Question on llvm-diff tool

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#1

Hello,

I’m using the ‘llvm-diff’ tool to diff two llvm assembly files. While doing that, I’ve observed that the ‘llvm-diff’ tool shows lots of diffs even when the same assembly files are given as command line arguments. For example, if we run

$ llvm-diff test.ll test.ll

‘llvm-diff’ shows lots of diffs for “static” global variables. This is an example.

// in test.c
static struct vmcs_layout vmcs_layout;

output for ‘llvm-diff’ is as follows.

%3 = load i32, i32* getelementptr inbounds (%struct.vmcs_layout.663, %struct.vmcs_layout.663* @vmcs_layout, i64 0, i32 0), align 4
< %3 = load i32, i32* getelementptr inbounds (%struct.vmcs_layout, %struct.vmcs_layout* @vmcs_layout, i64 0, i32 0), align 4

The difference is a suffix, 663. Is this behavior intentional for ‘llvm-diff’? If it’s intentional, how can I update ‘llvm-diff’ tool to see “no” diffs for the same .ll file?

Thank you,
Yonghyun

#2

Some context. Here are the type definitions and global definition:

%struct.vmcs_layout = type { i32, [2048 x %struct.vmcs_entry] }
%struct.vmcs_entry = type { i16, i16 }

…
@vmcs_layout = internal global %struct.vmcs_layout zeroinitializer, align 4, !dbg !10400

It seems like it’s applying the “.663” suffix because of a name clash with the other type.

-bw

#3

when diffing, perhaps we should compare the actual representation, tying same-name-and-structure objects together, though types arise from different parses, rather than the usually tighter scoping