[PowerPC] eliminate unconditional branch to the next instruction
This patch makes analyzeBranch eliminate unconditional branch to the next instruction.
After basic blocks are re-organized by optimizers, such as machine block placement, a BB may end with an unconditional branch to the next (fallthrough) BB. This patch removes such redundant branch instruction.
Differential Revision: https://reviews.llvm.org/D37730
llvm-svn: 314297
diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
index 80530ec..1e4cc4a 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -494,6 +494,20 @@
if (!isUnpredicatedTerminator(*I))
return false;
+ if (AllowModify) {
+ // If the BB ends with an unconditional branch to the fallthrough BB,
+ // we eliminate the branch instruction.
+ if (I->getOpcode() == PPC::B &&
+ MBB.isLayoutSuccessor(I->getOperand(0).getMBB())) {
+ I->eraseFromParent();
+
+ // We update iterator after deleting the last branch.
+ I = MBB.getLastNonDebugInstr();
+ if (I == MBB.end() || !isUnpredicatedTerminator(*I))
+ return false;
+ }
+ }
+
// Get the last instruction in the block.
MachineInstr &LastInst = *I;