[LLVMdev] labels commented out

[Sean Silva]

BB labels are implicitly assigned based on their position in the function.

This has come up before <
http://thread.gmane.org/gmane.comp.compilers.llvm.devel/62194/>, <
http://thread.gmane.org/gmane.comp.compilers.llvm.cvs/145768/>, r182332.

IIRC the only reason the label is in comments is that syntactically it's
not possible to put a numeric label name there. Otherwise just change
AssemblyWriter::printBasicBlock (in lib/IR/AsmWriter.cpp) to print out a
proper numeric label name instead of putting it in a comment.

-- Sean Silva


On Fri, Nov 1, 2013 at 3:39 PM, Preston Briggs <preston.briggs at gmail.com>wrote:

> I happened to try building LLVM without assertions today,
> and it changed the form of the LLVM IR that gets generated.
> Typically, I do something like
>
>     clang -O -emit-llvm -S Test.c
>
> For source like
>
> typedef struct node {
>   struct node *left;
>   struct node *right;
>   int key;
> } Tree;
>
> int sum(Tree *p) {
>   int s = 0;
>   if (p) {
>     s += sum(p->left);
>     s += sum(p->right);
>     s += p->key;
>   }
>   return s;
> }
>
> The resulting Test.s looks like
>
> define i32 @sum(%struct.node* %p) #0 {
>   %1 = icmp eq %struct.node* %p, null
>   br i1 %1, label %13, label %2
>
> ; <label>:2                                       ; preds = %0
>   %3 = getelementptr inbounds %struct.node* %p, i64 0, i32 0
>   %4 = load %struct.node** %3, align 8, !tbaa !0
>   %5 = tail call i32 @sum(%struct.node* %4)
>   %6 = getelementptr inbounds %struct.node* %p, i64 0, i32 1
>   %7 = load %struct.node** %6, align 8, !tbaa !0
>   %8 = tail call i32 @sum(%struct.node* %7)
>   %9 = add nsw i32 %8, %5
>   %10 = getelementptr inbounds %struct.node* %p, i64 0, i32 2
>   %11 = load i32* %10, align 4, !tbaa !3
>   %12 = add nsw i32 %9, %11
>   ret i32 %12
>
> ; <label>:13                                      ; preds = %0
>   ret i32 0
> }
>
>
> Note that labels %2 and %13 are not actually defined, though they're both
> referred to by the first branch and in comments.
>
> What's the deal?
>
> Thanks,
> Preston
>
>
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