[PATCH] D32323: [SimplifyCFG] Fix the determination of PostBB in conditional store merging to handle the targets on the second branch being commuted

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.

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.


https://reviews.llvm.org/D32323

Files:
  lib/Transforms/Utils/SimplifyCFG.cpp
  test/Transforms/SimplifyCFG/merge-cond-stores.ll


Index: test/Transforms/SimplifyCFG/merge-cond-stores.ll
===================================================================
--- test/Transforms/SimplifyCFG/merge-cond-stores.ll
+++ test/Transforms/SimplifyCFG/merge-cond-stores.ll
@@ -42,18 +42,13 @@
 ; 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
Index: lib/Transforms/Utils/SimplifyCFG.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyCFG.cpp
+++ lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3055,6 +3055,15 @@
   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 @@
   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())) ||


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