From e8e4921967994726e2e64c9906e23fec52f00cf7 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Wed, 25 Mar 2009 00:28:58 +0000
Subject: [PATCH] Fix PR3874 by restoring a condition I removed, but making it
 more precise than it used to be.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@67662 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/InstructionCombining.cpp    | 3 ++-
 test/Transforms/InstCombine/2009-03-24-InfLoop.ll | 9 +++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)
 create mode 100644 test/Transforms/InstCombine/2009-03-24-InfLoop.ll

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index f631d614573..1f80444632d 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -6582,7 +6582,8 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
       // preferable because it allows the C<<Y expression to be hoisted out
       // of a loop if Y is invariant and X is not.
       if (Shift && Shift->hasOneUse() && RHSV == 0 &&
-          ICI.isEquality() && !Shift->isArithmeticShift()) {
+          ICI.isEquality() && !Shift->isArithmeticShift() &&
+          !isa<Constant>(Shift->getOperand(0))) {
         // Compute C << Y.
         Value *NS;
         if (Shift->getOpcode() == Instruction::LShr) {
diff --git a/test/Transforms/InstCombine/2009-03-24-InfLoop.ll b/test/Transforms/InstCombine/2009-03-24-InfLoop.ll
new file mode 100644
index 00000000000..6d5a7bf77d2
--- /dev/null
+++ b/test/Transforms/InstCombine/2009-03-24-InfLoop.ll
@@ -0,0 +1,9 @@
+; PR3874
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis
+  define i1 @test(i32 %x) {
+    %A = lshr i32 3968, %x
+    %B = and i32 %A, 1
+    %C = icmp eq i32 %B, 0
+    ret i1 %C
+  }
+
-- 
2.34.1