From 2dd7657a5b063e6f77c34f418b7e23654b6fe4a0 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Sat, 23 Jan 2010 19:16:25 +0000
Subject: [PATCH] add an early out to ProcessBranchOnXOR to speed it up, handle
 the case when we can infer an input to the xor from all inputs that agree,
 instead of going into an infinite loop.  Another part of PR6199

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94321 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/JumpThreading.cpp | 25 +++++++++++++++++++++++
 test/Transforms/JumpThreading/crash.ll  | 27 +++++++++++++++++++++++++
 2 files changed, 52 insertions(+)

diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index 3a65c98195e..a7b4d157fcd 100644
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -1123,6 +1123,11 @@ bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) {
       isa<ConstantInt>(BO->getOperand(1)))
     return false;
   
+  // If the first instruction in BB isn't a phi, we won't be able to infer
+  // anything special about any particular predecessor.
+  if (!isa<PHINode>(BB->front()))
+    return false;
+  
   // If we have a xor as the branch input to this block, and we know that the
   // LHS or RHS of the xor in any predecessor is true/false, then we can clone
   // the condition into the predecessor and fix that value to true, saving some
@@ -1180,6 +1185,26 @@ bool JumpThreading::ProcessBranchOnXOR(BinaryOperator *BO) {
     BlocksToFoldInto.push_back(XorOpValues[i].second);
   }
   
+  // If we inferred a value for all of the predecessors, then duplication won't
+  // help us.  However, we can just replace the LHS or RHS with the constant.
+  if (BlocksToFoldInto.size() ==
+      cast<PHINode>(BB->front()).getNumIncomingValues()) {
+    if (SplitVal == 0) {
+      // If all preds provide undef, just nuke the xor, because it is undef too.
+      BO->replaceAllUsesWith(UndefValue::get(BO->getType()));
+      BO->eraseFromParent();
+    } else if (SplitVal->isZero()) {
+      // If all preds provide 0, replace the xor with the other input.
+      BO->replaceAllUsesWith(BO->getOperand(isLHS));
+      BO->eraseFromParent();
+    } else {
+      // If all preds provide 1, set the computed value to 1.
+      BO->setOperand(!isLHS, SplitVal);
+    }
+    
+    return true;
+  }
+  
   // Try to duplicate BB into PredBB.
   return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto);
 }
diff --git a/test/Transforms/JumpThreading/crash.ll b/test/Transforms/JumpThreading/crash.ll
index c0ef078ed20..ff980ffcc62 100644
--- a/test/Transforms/JumpThreading/crash.ll
+++ b/test/Transforms/JumpThreading/crash.ll
@@ -259,3 +259,30 @@ for.cond:                                         ; preds = %for.body, %lor.end
 for.body:                                         ; preds = %for.cond
   br label %for.cond
 }
+
+; PR6119
+define i32 @test9(i32 %action) nounwind {
+entry:
+  switch i32 %action, label %lor.rhs [
+    i32 1, label %if.then
+    i32 0, label %lor.end
+  ]
+
+if.then:                                          ; preds = %for.cond, %lor.end, %entry
+  ret i32 undef
+
+lor.rhs:                                          ; preds = %entry
+  br label %lor.end
+
+lor.end:                                          ; preds = %lor.rhs, %entry
+  %0 = phi i1 [ undef, %lor.rhs ], [ true, %entry ] ; <i1> [#uses=1]
+  %cmp103 = xor i1 undef, %0                      ; <i1> [#uses=1]
+  br i1 %cmp103, label %for.cond, label %if.then
+
+for.cond:                                         ; preds = %for.body, %lor.end
+  br i1 undef, label %if.then, label %for.body
+
+for.body:                                         ; preds = %for.cond
+  br label %for.cond
+}
+