[PATCH] D116424: [ShrinkWrap] don't sink Save points past INLINEASM_BR MachineInstrs

[Nick Desaulniers via Phabricator via llvm-commits]

nickdesaulniers added inline comments.


================
Comment at: llvm/lib/CodeGen/ShrinkWrap.cpp:507-511
+      if (MI.getOpcode() == TargetOpcode::INLINEASM_BR) {
+        LLVM_DEBUG(dbgs() << "inlineasm_br prevents shrink-wrapping\n");
+        return false;
+      }
       if (!useOrDefCSROrFI(MI, RS.get()))
----------------
nickdesaulniers wrote:
> There's something simpler going on here.  The same exact input works as expected for other architectures with link registers, such as `arm` and `aarch64`. It seems that `useOrDefCSROrFI` is returning `true` for the `INLINEASM_BR` for those architectures, but not `powerpc64le`.
In `aarch64` and `arm`, the `MachineOperand` `useOrDefCSROrFI` is interested is marked `dead`, but for `ppc64le` it's not.

`implicit-def dead early-clobber $lr` (arm, aarch64)
`implicit-def early-clobber $lr` (ppc64le)

For `arm` and `aarch64`, the `MachineOperand` is marked dead by the `livevars` pass. For ppc64le, it does not.

---

Also, within `useOrDefCSROrFI`, the call to `RCI.getLastCalleeSavedAlias` returns 0 on ppc, unlike aarch64 and arm.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D116424/new/

https://reviews.llvm.org/D116424