[llvm] 5502cfa - [LoopUnswitch] Trivial simplification: remove trivial dead condition after unswitch

[Serguei Katkov via llvm-commits]

Author: Serguei Katkov
Date: 2020-09-22T09:04:59+07:00
New Revision: 5502cfa091e0f6b35a6d96435b2ec15a43a324eb

URL: https://github.com/llvm/llvm-project/commit/5502cfa091e0f6b35a6d96435b2ec15a43a324eb
DIFF: https://github.com/llvm/llvm-project/commit/5502cfa091e0f6b35a6d96435b2ec15a43a324eb.diff

LOG: [LoopUnswitch] Trivial simplification: remove trivial dead condition after unswitch

Non trivial loop unswitch can keep the dead condition instruction.
CL adds trivial dead code elimination for unused condition.

Reviewers: asbirlea, aqjune, fhahn, DaniilSuchkov, reames
Reviewed By: asbirlea
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D88014

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
    llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch.ll

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
index 6656fa0670f5..55d790cd051f 100644
--- a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -50,6 +50,7 @@
 #include "llvm/Transforms/Scalar/SimpleLoopUnswitch.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Cloning.h"
+#include "llvm/Transforms/Utils/Local.h"
 #include "llvm/Transforms/Utils/LoopUtils.h"
 #include "llvm/Transforms/Utils/ValueMapper.h"
 #include <algorithm>
@@ -1139,9 +1140,22 @@ static BasicBlock *buildClonedLoopBlocks(
   // Replace the cloned branch with an unconditional branch to the cloned
   // unswitched successor.
   auto *ClonedSuccBB = cast<BasicBlock>(VMap.lookup(UnswitchedSuccBB));
-  ClonedParentBB->getTerminator()->eraseFromParent();
+  Instruction *ClonedTerminator = ClonedParentBB->getTerminator();
+  // Trivial Simplification. If Terminator is a conditional branch and
+  // condition becomes dead - erase it.
+  Value *ClonedConditionToErase = nullptr;
+  if (auto *BI = dyn_cast<BranchInst>(ClonedTerminator))
+    ClonedConditionToErase = BI->getCondition();
+  else if (auto *SI = dyn_cast<SwitchInst>(ClonedTerminator))
+    ClonedConditionToErase = SI->getCondition();
+
+  ClonedTerminator->eraseFromParent();
   BranchInst::Create(ClonedSuccBB, ClonedParentBB);
 
+  if (ClonedConditionToErase)
+    RecursivelyDeleteTriviallyDeadInstructions(ClonedConditionToErase, nullptr,
+                                               MSSAU);
+
   // If there are duplicate entries in the PHI nodes because of multiple edges
   // to the unswitched successor, we need to nuke all but one as we replaced it
   // with a direct branch.

diff  --git a/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch.ll b/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch.ll
index 0aec52d447d5..6fff85a2255c 100644
--- a/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch.ll
+++ b/llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch.ll
@@ -2720,8 +2720,6 @@ loop_a:
 ; CHECK-NEXT:    br label %loop_begin.us
 ;
 ; CHECK:       loop_begin.us:
-; CHECK-NEXT:    %[[V1_US:.*]] = load i1, i1* %ptr
-; CHECK-NEXT:    %[[OR_US:.*]] = or i1 %[[V1_US]], true
 ; CHECK-NEXT:    br label %loop_a.us
 ;
 ; CHECK:       loop_a.us:
@@ -2796,12 +2794,6 @@ loop_begin:
 ; CHECK-NEXT:    br label %loop_begin.us
 ;
 ; CHECK:       loop_begin.us:
-; CHECK-NEXT:    %[[V1_US:.*]] = load i1, i1* %ptr1
-; CHECK-NEXT:    %[[V2_US:.*]] = load i1, i1* %ptr2
-; CHECK-NEXT:    %[[AND1_US:.*]] = and i1 %[[V1_US]], %cond1
-; CHECK-NEXT:    %[[OR1_US:.*]] = or i1 %[[V2_US]], %cond2
-; CHECK-NEXT:    %[[AND2_US:.*]] = and i1 %[[AND1_US]], %[[OR1_US]]
-; CHECK-NEXT:    %[[AND3_US:.*]] = and i1 %[[AND2_US]], %cond3
 ; CHECK-NEXT:    br label %loop_b.us
 ;
 ; CHECK:       loop_b.us:
@@ -2883,12 +2875,6 @@ loop_begin:
 ; CHECK-NEXT:    br label %loop_begin.us
 ;
 ; CHECK:       loop_begin.us:
-; CHECK-NEXT:    %[[V1_US:.*]] = load i1, i1* %ptr1
-; CHECK-NEXT:    %[[V2_US:.*]] = load i1, i1* %ptr2
-; CHECK-NEXT:    %[[OR1_US:.*]] = or i1 %[[V1_US]], %cond1
-; CHECK-NEXT:    %[[AND1_US:.*]] = and i1 %[[V2_US]], %cond2
-; CHECK-NEXT:    %[[OR2_US:.*]] = or i1 %[[OR1_US]], %[[AND1_US]]
-; CHECK-NEXT:    %[[OR3_US:.*]] = or i1 %[[OR2_US]], %cond3
 ; CHECK-NEXT:    br label %loop_b.us
 ;
 ; CHECK:       loop_b.us: