nickdesaulniers added inline comments.
================
Comment at: clang/lib/CodeGen/CGStmt.cpp:2868-2873
+ // If we happen to share the same indirect and default dest, don't re-add
+ // stores. That was done for the default destination in the above call to
+ // EmitAsmStores.
+ llvm::BasicBlock *Succ = CBR->getIndirectDest(i);
+ if (Succ == CBR->getDefaultDest())
+ continue;
----------------
void wrote:
> nickdesaulniers wrote:
> > nickdesaulniers wrote:
> > > I'm not sure that I need to handle this case (of a callbr with the same
> > > indirect destination as the default destination). That might result from
> > > optimizations, but I don't think clang can or will generate such IR.
> > > Maybe I should turn this into an: `assert(CBR->getIndirectDest(i) !=
> > > CBR->getDefaultDest(i) && "We already emitted asm stores in the default
> > > dest");`?
> > Yeah, it's impossible. While a CallBrInst can have a same indirect
> > destination as the default destination as a result of optimizations, above
> > we always create an `"asm.fallthrough"` block that is distinct from any of
> > the named labels from the `asm goto`.
> It could only happen with something like this:
>
> ```
> asm goto (... :::: indirect);
>
> indirect:;
> ```
>
> In that simplified case, it looks like clang emits this:
>
> ```
> define dso_local void @foo() #0 {
> callbr void asm sideeffect "", "i,~{dirflag},~{fpsr},~{flags}"(i8*
> blockaddress(@foo, %2)) #1
> to label %1 [label %2], !srcloc !6
>
> 1: ; preds = %0
> br label %2
>
> 2: ; preds = %1, %0
> ret void
> }
> ```
>
> So it's probably safe to make this an assert.
Oh, it's not just the default and indirects sharing, but what if the same
indirect is listed twice? I should add a test for that...i.e.
```
asm goto (... :::: indirect,indirect);
```
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D136497/new/
https://reviews.llvm.org/D136497
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