Implementation of asm-goto support in LLVM

This patch accompanies the RFC posted here:
http://lists.llvm.org/pipermail/llvm-dev/2018-October/127239.html

This patch adds a new CallBr IR instruction to support asm-goto
inline assembly like gcc as used by the linux kernel. This
instruction is both a call instruction and a terminator
instruction with multiple successors. Only inline assembly
usage is supported today.

This also adds a new INLINEASM_BR opcode to SelectionDAG and
MachineIR to represent an INLINEASM block that is also
considered a terminator instruction.

There will likely be more bug fixes and optimizations to follow
this, but we felt it had reached a point where we would like to
switch to an incremental development model.

Patch by Craig Topper, Alexander Ivchenko, Mikhail Dvoretckii

Differential Revision: https://reviews.llvm.org/D53765

llvm-svn: 353563

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 70812dc..062bbcd 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -996,6 +996,18 @@ bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
     }
   }
 
+  // We cannot fold the block if it's a branch to an already present callbr
+  // successor because that creates duplicate successors.
+  for (auto I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
+    if (auto *CBI = dyn_cast<CallBrInst>((*I)->getTerminator())) {
+      if (Succ == CBI->getDefaultDest())
+        return false;
+      for (unsigned i = 0, e = CBI->getNumIndirectDests(); i != e; ++i)
+        if (Succ == CBI->getIndirectDest(i))
+          return false;
+    }
+  }
+
   LLVM_DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
 
   SmallVector<DominatorTree::UpdateType, 32> Updates;