[PATCH] D136497: [Clang] support for outputs along indirect edges of asm goto

[Bill Wendling via Phabricator via cfe-commits]

void 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;
----------------
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");`?
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.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D136497/new/

https://reviews.llvm.org/D136497