[PATCH] D63972: [PowerPC] Do the Early Return for the li and unconditional branch

[Zhang Kang via Phabricator via llvm-commits]

ZhangKang updated this revision to Diff 210495.
ZhangKang marked an inline comment as done.
ZhangKang added a comment.

Modify the comments and add test.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D63972/new/

https://reviews.llvm.org/D63972

Files:
  llvm/lib/CodeGen/MachineBlockPlacement.cpp
  llvm/test/CodeGen/PowerPC/block-placement-1.mir
  llvm/test/CodeGen/PowerPC/block-placement.mir


Index: llvm/test/CodeGen/PowerPC/block-placement.mir
===================================================================
--- llvm/test/CodeGen/PowerPC/block-placement.mir
+++ llvm/test/CodeGen/PowerPC/block-placement.mir
@@ -209,14 +209,14 @@
     BLR8 implicit $lr8, implicit $rm, implicit killed $x3
 
   ; CHECK:      bb.5.if.else.i:
-  ; CHECK:        successors: %bb.11(0x80000000)
-  ; CHECK:        B %bb.11
+  ; CHECK-NOT:    successors: %bb.11(0x80000000)
+  ; CHECK-NOT:    B %bb.11
+  ; CHECK:        renamable $x3 = LI8 1
+  ; CHECK-NEXT:   BLR8 implicit $lr8, implicit $rm, implicit killed $x3
 
   ; CHECK:      bb.8.while.body.i (align 4):
-  ; CHECK:        successors: %bb.11(0x04000000), %bb.9(0x7c000000)
-  ; CHECK:        BCC 76, killed renamable $cr0, %bb.11
+  ; CHECK:        successors: %bb.5(0x04000000), %bb.9(0x7c000000)
+  ; CHECK:        BCC 76, killed renamable $cr0, %bb.5
 
-  ; CHECK:      bb.11:
-  ; CHECK:        renamable $x3 = LI8 1
-  ; CHECK-NEXT:   BLR8 implicit $lr8, implicit $rm, implicit killed $x3
+  ; CHECK-NOT:      bb.11:
 ...
Index: llvm/test/CodeGen/PowerPC/block-placement-1.mir
===================================================================
--- llvm/test/CodeGen/PowerPC/block-placement-1.mir
+++ llvm/test/CodeGen/PowerPC/block-placement-1.mir
@@ -299,14 +299,14 @@
   bb.11.unreachable:
 
   ; CHECK:      bb.1.for.body:
-  ; CHECK:        successors: %bb.2(0x7ffff800), %bb.3(0x00000800)
-  ; CHECK:        B %bb.2
+  ; CHECK:        successors: %bb.3(0x00000800)
+  ; CHECK-NOT:        B %bb.2
 
   ; CHECK:      bb.4.catch4:
-  ; CHECK:        successors: %bb.11(0x7ffff800), %bb.6(0x00000800)
-  ; CHECK:        B %bb.11
+  ; CHECK:        %bb.6(0x00000800)
+  ; CHECK-NOT:    B %bb.11
 
-  ; CHECK:      bb.2..noexc:
+  ; CHECK-NOT:  bb.2..noexc:
 
-  ; CHECK:      bb.11.unreachable: 
+  ; CHECK-NOT:  bb.11.unreachable: 
 ...
Index: llvm/lib/CodeGen/MachineBlockPlacement.cpp
===================================================================
--- llvm/lib/CodeGen/MachineBlockPlacement.cpp
+++ llvm/lib/CodeGen/MachineBlockPlacement.cpp
@@ -2730,6 +2730,30 @@
         TII->removeBranch(*ChainBB);
         TII->insertBranch(*ChainBB, FBB, TBB, Cond, dl);
         ChainBB->updateTerminator();
+      } else if (Cond.empty() && TBB && ChainBB != TBB && 
+                 !TBB->canFallThrough()) {
+        // When ChainBB is unconditional branch to the TBB, and TBB has no 
+        // fallthrough predecessor and fallthrough successor, if ChainBB has
+        // only one unconditonal branch or TBB has only one predecessor. We can
+        // do the tail duplication for ChainBB and remove TBB.
+        MachineFunction::iterator I(TBB);
+        if (((TBB == &*F->begin()) || !std::prev(I)->canFallThrough()) &&
+             (TailDup.isSimpleBB(ChainBB) || (TBB->pred_size() == 1))) {
+          TII->removeBranch(*ChainBB);
+          ChainBB->removeSuccessor(TBB);
+
+          // Update the CFG.
+          for (MachineBasicBlock::pred_iterator PI = TBB->pred_begin(),
+               PE = TBB->pred_end(); PI != PE; PI++) 
+            (*PI)->ReplaceUsesOfBlockWith(TBB, ChainBB);
+
+          for (MachineBasicBlock *Succ : TBB->successors())
+            ChainBB->addSuccessor(Succ, MBPI->getEdgeProbability(TBB, Succ));
+
+          // Move all the instructions of TBB to ChainBB.
+          ChainBB->splice(ChainBB->end(), TBB, TBB->begin(), TBB->end());
+          F->remove(TBB);
+        }
       }
     }
   }


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