Generalize MergeBlockIntoPredecessor. Replace uses of MergeBasicBlockIntoOnlyPred.

Summary:
Two utils methods have essentially the same functionality. This is an attempt to merge them into one.
1. lib/Transforms/Utils/Local.cpp : MergeBasicBlockIntoOnlyPred
2. lib/Transforms/Utils/BasicBlockUtils.cpp : MergeBlockIntoPredecessor

Prior to the patch:
1. MergeBasicBlockIntoOnlyPred
Updates either DomTree or DeferredDominance
Moves all instructions from Pred to BB, deletes Pred
Asserts BB has single predecessor
If address was taken, replace the block address with constant 1 (?)

2. MergeBlockIntoPredecessor
Updates DomTree, LoopInfo and MemoryDependenceResults
Moves all instruction from BB to Pred, deletes BB
Returns if doesn't have a single predecessor
Returns if BB's address was taken

After the patch:
Method 2. MergeBlockIntoPredecessor is attempting to become the new default:
Updates DomTree or DeferredDominance, and LoopInfo and MemoryDependenceResults
Moves all instruction from BB to Pred, deletes BB
Returns if doesn't have a single predecessor
Returns if BB's address was taken

Uses of MergeBasicBlockIntoOnlyPred that need to be replaced:

1. lib/Transforms/Scalar/LoopSimplifyCFG.cpp
Updated in this patch. No challenges.

2. lib/CodeGen/CodeGenPrepare.cpp
Updated in this patch.
  i. eliminateFallThrough is straightforward, but I added using a temporary array to avoid the iterator invalidation.
  ii. eliminateMostlyEmptyBlock(s) methods also now use a temporary array for blocks
Some interesting aspects:
  - Since Pred is not deleted (BB is), the entry block does not need updating.
  - The entry block was being updated with the deleted block in eliminateMostlyEmptyBlock. Added assert to make obvious that BB=SinglePred.
  - isMergingEmptyBlockProfitable assumes BB is the one to be deleted.
  - eliminateMostlyEmptyBlock(BB) does not delete BB on one path, it deletes its unique predecessor instead.
  - adding some test owner as subscribers for the interesting tests modified:
    test/CodeGen/X86/avx-cmp.ll
    test/CodeGen/AMDGPU/nested-loop-conditions.ll
    test/CodeGen/AMDGPU/si-annotate-cf.ll
    test/CodeGen/X86/hoist-spill.ll
    test/CodeGen/X86/2006-11-17-IllegalMove.ll

3. lib/Transforms/Scalar/JumpThreading.cpp
Not covered in this patch. It is the only use case using the DeferredDominance.
I would defer to Brian Rzycki to make this replacement.

Reviewers: chandlerc, spatel, davide, brzycki, bkramer, javed.absar

Subscribers: qcolombet, sanjoy, nemanjai, nhaehnle, jlebar, tpr, kbarton, RKSimon, wmi, arsenm, llvm-commits

Differential Revision: https://reviews.llvm.org/D48202

llvm-svn: 335183

1 files changed, 4 insertions, 4 deletions

diff --git a/llvm/test/Transforms/SimpleLoopUnswitch/trivial-unswitch-iteration.ll b/llvm/test/Transforms/SimpleLoopUnswitch/trivial-unswitch-iteration.ll
index 7ccd89a3606..6c409e40b28 100644
--- a/llvm/test/Transforms/SimpleLoopUnswitch/trivial-unswitch-iteration.ll
+++ b/llvm/test/Transforms/SimpleLoopUnswitch/trivial-unswitch-iteration.ll
@@ -13,7 +13,7 @@ entry:
 ; CHECK-NEXT:    br i1 %{{.*}}, label %entry.split.split, label %loop_exit
 ;
 ; CHECK:       entry.split.split:
-; CHECK-NEXT:    br label %do_something
+; CHECK-NEXT:    br label %loop_begin
 
 loop_begin:
   br i1 %cond1, label %continue, label %loop_exit ; first trivial condition
@@ -27,9 +27,9 @@ continue:
 do_something:
   call void @some_func() noreturn nounwind
   br label %loop_begin
-; CHECK:       do_something:
+; CHECK:       loop_begin:
 ; CHECK-NEXT:    call
-; CHECK-NEXT:    br label %do_something
+; CHECK-NEXT:    br label %loop_begin
 
 loop_exit:
   ret i32 0
@@ -38,4 +38,4 @@ loop_exit:
 ;
 ; CHECK:       loop_exit.split:
 ; CHECK-NEXT:    ret
-}
\ No newline at end of file
+}