From a4b389c12505acb4126135a385ee7c59553940a9 Mon Sep 17 00:00:00 2001
From: Daniel Jasper <djasper@google.com>
Date: Mon, 30 Mar 2015 09:30:02 +0000
Subject: [PATCH] Revert "[SCEV] Look at backedge dominating conditions."

This leads to terribly slow compile times under MSAN. More discussion
on the commit thread of r233447.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233529 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ScalarEvolution.cpp              | 40 --------------
 .../latch-dominating-conditions.ll            | 55 -------------------
 2 files changed, 95 deletions(-)
 delete mode 100644 test/Analysis/ScalarEvolution/latch-dominating-conditions.ll

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 26b468013c6..4e713fb1218 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -6686,46 +6686,6 @@ ScalarEvolution::isLoopBackedgeGuardedByCond(const Loop *L,
                     LoopContinuePredicate->getSuccessor(0) != L->getHeader()))
     return true;
 
-  // If the loop is not reachable from the entry block, we risk running into an
-  // infinite loop as we walk up into the dom tree.  These loops do not matter
-  // anyway, so we just return a conservative answer when we see them.
-  if (!DT->isReachableFromEntry(L->getHeader()))
-    return false;
-
-  for (DomTreeNode *DTN = (*DT)[Latch], *HeaderDTN = (*DT)[L->getHeader()];
-       DTN != HeaderDTN;
-       DTN = DTN->getIDom()) {
-
-    assert(DTN && "should reach the loop header before reaching the root!");
-
-    BasicBlock *BB = DTN->getBlock();
-    BasicBlock *PBB = BB->getSinglePredecessor();
-    if (!PBB)
-      continue;
-
-    BranchInst *ContinuePredicate = dyn_cast<BranchInst>(PBB->getTerminator());
-    if (!ContinuePredicate || !ContinuePredicate->isConditional())
-      continue;
-
-    Value *Condition = ContinuePredicate->getCondition();
-
-    // If we have an edge `E` within the loop body that dominates the only
-    // latch, the condition guarding `E` also guards the backedge.  This
-    // reasoning works only for loops with a single latch.
-
-    BasicBlockEdge DominatingEdge(PBB, BB);
-    if (DominatingEdge.isSingleEdge()) {
-      // We're constructively (and conservatively) enumerating edges within the
-      // loop body that dominate the latch.  The dominator tree better agree
-      // with us on this:
-      assert(DT->dominates(DominatingEdge, Latch) && "should be!");
-
-      if (isImpliedCond(Pred, LHS, RHS, Condition,
-                        BB != ContinuePredicate->getSuccessor(0)))
-        return true;
-    }
-  }
-
   // Check conditions due to any @llvm.assume intrinsics.
   for (auto &AssumeVH : AC->assumptions()) {
     if (!AssumeVH)
diff --git a/test/Analysis/ScalarEvolution/latch-dominating-conditions.ll b/test/Analysis/ScalarEvolution/latch-dominating-conditions.ll
deleted file mode 100644
index 3f6f9584cce..00000000000
--- a/test/Analysis/ScalarEvolution/latch-dominating-conditions.ll
+++ /dev/null
@@ -1,55 +0,0 @@
-; RUN: opt -S -indvars < %s | FileCheck %s
-
-declare void @side_effect(i1)
-
-define void @latch_dominating_0(i8 %start) {
-; CHECK-LABEL: latch_dominating_0
- entry:
-  %e = icmp slt i8 %start, 42
-  br i1 %e, label %loop, label %exit
-
- loop:
-; CHECK-LABEL: loop
-  %idx = phi i8 [ %start, %entry ], [ %idx.inc, %be ]
-  %idx.inc = add i8 %idx, 1
-  %folds.to.true = icmp slt i8 %idx, 42
-; CHECK: call void @side_effect(i1 true)
-  call void @side_effect(i1 %folds.to.true)
-  %c0 = icmp slt i8 %idx.inc, 42
-  br i1 %c0, label %be, label %exit
-
- be:
-; CHECK: call void @side_effect(i1 true)
-  call void @side_effect(i1 %folds.to.true)
-  %c1 = icmp slt i8 %idx.inc, 100
-  br i1 %c1, label %loop, label %exit
-
- exit:
-  ret void
-}
-
-define void @latch_dominating_1(i8 %start) {
-; CHECK-LABEL: latch_dominating_1
- entry:
-  %e = icmp slt i8 %start, 42
-  br i1 %e, label %loop, label %exit
-
- loop:
-; CHECK-LABEL: loop
-  %idx = phi i8 [ %start, %entry ], [ %idx.inc, %be ]
-  %idx.inc = add i8 %idx, 1
-  %does.not.fold.to.true = icmp slt i8 %idx, 42
-; CHECK: call void @side_effect(i1 %does.not.fold.to.true)
-  call void @side_effect(i1 %does.not.fold.to.true)
-  %c0 = icmp slt i8 %idx.inc, 42
-  br i1 %c0, label %be, label %be
-
- be:
-; CHECK: call void @side_effect(i1 %does.not.fold.to.true)
-  call void @side_effect(i1 %does.not.fold.to.true)
-  %c1 = icmp slt i8 %idx.inc, 100
-  br i1 %c1, label %loop, label %exit
-
- exit:
-  ret void
-}