[IRTranslator] Merge the entry and ABI lowering blocks.
The IRTranslator uses an additional block before the LLVM-IR entry block
to perform all the ABI lowering and the constant hoisting. Thus, this
block is the actual entry block and it falls through the LLVM-IR entry
block. However, with such representation, we end up with two basic
blocks that are not maximal.
Therefore, this patch adds a bit of canonicalization by merging both the
LLVM-IR entry block and the ABI lowering/constants hoisting into one
block, making the resulting block more likely to be maximal (indeed the
LLVM-IR entry block might not have been maximal).
llvm-svn: 289891
diff --git a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
index 936e1b8..cf35afb 100644
--- a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -815,6 +815,32 @@
// Now that the MachineFrameInfo has been configured, no further changes to
// the reserved registers are possible.
MRI->freezeReservedRegs(*MF);
+
+ // Merge the argument lowering and constants block with its single
+ // successor, the LLVM-IR entry block. We want the basic block to
+ // be maximal.
+ assert(EntryBB->succ_size() == 1 &&
+ "Custom BB used for lowering should have only one successor");
+ // Get the successor of the current entry block.
+ MachineBasicBlock &NewEntryBB = **EntryBB->succ_begin();
+ assert(NewEntryBB.pred_size() == 1 &&
+ "LLVM-IR entry block has a predecessor!?");
+ // Move all the instruction from the current entry block to the
+ // new entry block.
+ NewEntryBB.splice(NewEntryBB.begin(), EntryBB, EntryBB->begin(),
+ EntryBB->end());
+
+ // Update the live-in information for the new entry block.
+ for (const MachineBasicBlock::RegisterMaskPair &LiveIn : EntryBB->liveins())
+ NewEntryBB.addLiveIn(LiveIn);
+ NewEntryBB.sortUniqueLiveIns();
+
+ // Get rid of the now empty basic block.
+ EntryBB->removeSuccessor(&NewEntryBB);
+ MF->remove(EntryBB);
+
+ assert(&MF->front() == &NewEntryBB &&
+ "New entry wasn't next in the list of basic block!");
}
finalizeFunction();