[llvm] r300992 - [SimplifyCFG] Fix the determination of PostBB in conditional store merging to handle the targets on the second branch being commuted

[Craig Topper via llvm-commits]

Author: ctopper
Date: Fri Apr 21 10:53:42 2017
New Revision: 300992

URL: http://llvm.org/viewvc/llvm-project?rev=300992&view=rev
Log:
[SimplifyCFG] Fix the determination of PostBB in conditional store merging to handle the targets on the second branch being commuted

Currently we choose PostBB as the single successor of QFB, but its possible that QTB's single successor is QFB which would make QFB the correct choice.

Differential Revision: https://reviews.llvm.org/D32323

Modified:
    llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
    llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores.ll

Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=300992&r1=300991&r2=300992&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Fri Apr 21 10:53:42 2017
@@ -3055,6 +3055,15 @@ static bool mergeConditionalStores(Branc
   BasicBlock *QFB = QBI->getSuccessor(1);
   BasicBlock *PostBB = QFB->getSingleSuccessor();
 
+  // Make sure we have a good guess for PostBB. If QTB's only successor is
+  // QFB, then QFB is a better PostBB.
+  if (QTB->getSingleSuccessor() == QFB)
+    PostBB = QFB;
+
+  // If we couldn't find a good PostBB, stop.
+  if (!PostBB)
+    return false;
+
   bool InvertPCond = false, InvertQCond = false;
   // Canonicalize fallthroughs to the true branches.
   if (PFB == QBI->getParent()) {
@@ -3079,8 +3088,7 @@ static bool mergeConditionalStores(Branc
   auto HasOnePredAndOneSucc = [](BasicBlock *BB, BasicBlock *P, BasicBlock *S) {
     return BB->getSinglePredecessor() == P && BB->getSingleSuccessor() == S;
   };
-  if (!PostBB ||
-      !HasOnePredAndOneSucc(PFB, PBI->getParent(), QBI->getParent()) ||
+  if (!HasOnePredAndOneSucc(PFB, PBI->getParent(), QBI->getParent()) ||
       !HasOnePredAndOneSucc(QFB, QBI->getParent(), PostBB))
     return false;
   if ((PTB && !HasOnePredAndOneSucc(PTB, PBI->getParent(), QBI->getParent())) ||

Modified: llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores.ll?rev=300992&r1=300991&r2=300992&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/merge-cond-stores.ll Fri Apr 21 10:53:42 2017
@@ -37,23 +37,17 @@ end:
 }
 
 ; This is the same as test_simple, but the branch target order has been swapped
-; TODO: This test should succeed and end up if-converted.
 define void @test_simple_commuted(i32* %p, i32 %a, i32 %b) {
 ; CHECK-LABEL: @test_simple_commuted(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[X1:%.*]] = icmp eq i32 [[A:%.*]], 0
-; CHECK-NEXT:    br i1 [[X1]], label [[YES1:%.*]], label [[FALLTHROUGH:%.*]]
-; CHECK:       yes1:
-; CHECK-NEXT:    store i32 0, i32* [[P:%.*]], align 4
-; CHECK-NEXT:    br label [[FALLTHROUGH]]
-; CHECK:       fallthrough:
 ; CHECK-NEXT:    [[X2:%.*]] = icmp eq i32 [[B:%.*]], 0
-; CHECK-NEXT:    br i1 [[X2]], label [[YES2:%.*]], label [[END:%.*]]
-; CHECK:       yes2:
-; CHECK-NEXT:    store i32 1, i32* [[P]], align 4
-; CHECK-NEXT:    br label [[END]]
-; CHECK:       end:
-; CHECK-NEXT:    ret void
+; CHECK-NEXT:    [[TMP0:%.*]] = or i1 [[X1]], [[X2]]
+; CHECK-NEXT:    br i1 [[TMP0]], label [[TMP1:%.*]], label [[TMP2:%.*]]
+; CHECK:         [[DOT:%.*]] = zext i1 [[X2]] to i32
+; CHECK-NEXT:    store i32 [[DOT]], i32* [[P:%.*]], align 4
+; CHECK-NEXT:    br label [[TMP2]]
+; CHECK:         ret void
 ;
 entry:
   %x1 = icmp eq i32 %a, 0