Index: llvm/trunk/lib/Transforms/Utils/SimplifyIndVar.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ llvm/trunk/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -521,20 +521,19 @@
     if (isa<Instruction>(U) &&
         !DT->isReachableFromEntry(cast<Instruction>(U)->getParent()))
       continue;
-    if (ICmpInst *ICI = dyn_cast<ICmpInst>(U)) {
-      if (ICI->getOperand(0) == TI && L->isLoopInvariant(ICI->getOperand(1))) {
-        assert(L->contains(ICI->getParent()) && "LCSSA form broken?");
-        // If we cannot get rid of trunc, bail.
-        if (ICI->isSigned() && !DoesSExtCollapse)
-          return false;
-        if (ICI->isUnsigned() && !DoesZExtCollapse)
-          return false;
-        // For equality, either signed or unsigned works.
-        ICmpUsers.push_back(ICI);
-      } else
-        return false;
-    } else
+    ICmpInst *ICI = dyn_cast<ICmpInst>(U);
+    if (!ICI) return false;
+    assert(L->contains(ICI->getParent()) && "LCSSA form broken?");
+    if (!(ICI->getOperand(0) == TI && L->isLoopInvariant(ICI->getOperand(1))) &&
+        !(ICI->getOperand(1) == TI && L->isLoopInvariant(ICI->getOperand(0))))
       return false;
+    // If we cannot get rid of trunc, bail.
+    if (ICI->isSigned() && !DoesSExtCollapse)
+      return false;
+    if (ICI->isUnsigned() && !DoesZExtCollapse)
+      return false;
+    // For equality, either signed or unsigned works.
+    ICmpUsers.push_back(ICI);
   }
 
   auto CanUseZExt = [&](ICmpInst *ICI) {
@@ -557,7 +556,8 @@
   };
   // Replace all comparisons against trunc with comparisons against IV.
   for (auto *ICI : ICmpUsers) {
-    auto *Op1 = ICI->getOperand(1);
+    bool IsSwapped = L->isLoopInvariant(ICI->getOperand(0));
+    auto *Op1 = IsSwapped ? ICI->getOperand(0) : ICI->getOperand(1);
     Instruction *Ext = nullptr;
     // For signed/unsigned predicate, replace the old comparison with comparison
     // of immediate IV against sext/zext of the invariant argument. If we can
@@ -566,6 +566,7 @@
     // TODO: If we see a signed comparison which can be turned into unsigned,
     // we can do it here for canonicalization purposes.
     ICmpInst::Predicate Pred = ICI->getPredicate();
+    if (IsSwapped) Pred = ICmpInst::getSwappedPredicate(Pred);
     if (CanUseZExt(ICI)) {
       assert(DoesZExtCollapse && "Unprofitable zext?");
       Ext = new ZExtInst(Op1, IVTy, "zext", ICI);
Index: llvm/trunk/test/Transforms/IndVarSimplify/eliminate-trunc.ll
===================================================================
--- llvm/trunk/test/Transforms/IndVarSimplify/eliminate-trunc.ll
+++ llvm/trunk/test/Transforms/IndVarSimplify/eliminate-trunc.ll
@@ -561,4 +561,108 @@
   ret void
 }
 
+define void @test_13a(i32 %n) {
+;
+; CHECK-LABEL: @test_13a(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[ZEXT:%.*]] = zext i32 1024 to i64
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i64 [[IV]], 2
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp ne i64 [[IV]], [[ZEXT]]
+; CHECK-NEXT:    br i1 [[TMP0]], label [[LOOP]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  %iv.next = add nsw nuw i64 %iv, 2
+  %narrow.iv = trunc i64 %iv to i32
+  %cmp = icmp ne i32 1024, %narrow.iv
+  br i1 %cmp, label %loop, label %exit
+exit:
+  ret void
+}
+
+define void @test_13b(i32 %n) {
+;
+; CHECK-LABEL: @test_13b(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[ZEXT:%.*]] = zext i32 1024 to i64
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i64 [[IV]], 2
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp ult i64 [[IV]], [[ZEXT]]
+; CHECK-NEXT:    br i1 [[TMP0]], label [[LOOP]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  %iv.next = add nsw nuw i64 %iv, 2
+  %narrow.iv = trunc i64 %iv to i32
+  %cmp = icmp ugt i32 1024, %narrow.iv
+  br i1 %cmp, label %loop, label %exit
+exit:
+  ret void
+}
+
+define void @test_13c(i32 %n) {
+;
+; CHECK-LABEL: @test_13c(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[ZEXT:%.*]] = zext i32 1024 to i64
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i64 [[IV]], 2
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp ult i64 [[IV]], [[ZEXT]]
+; CHECK-NEXT:    br i1 [[TMP0]], label [[LOOP]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop
+loop:
+  %iv = phi i64 [ 0, %entry ], [ %iv.next, %loop ]
+  %iv.next = add nsw nuw i64 %iv, 2
+  %narrow.iv = trunc i64 %iv to i32
+  %cmp = icmp sgt i32 1024, %narrow.iv
+  br i1 %cmp, label %loop, label %exit
+exit:
+  ret void
+}
+
+define void @test_13d(i32 %n) {
+;
+; CHECK-LABEL: @test_13d(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SEXT:%.*]] = sext i32 1024 to i64
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ -20, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[IV_NEXT]] = add nsw i64 [[IV]], 2
+; CHECK-NEXT:    [[TMP0:%.*]] = icmp slt i64 [[IV]], [[SEXT]]
+; CHECK-NEXT:    br i1 [[TMP0]], label [[LOOP]], label [[EXIT:%.*]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %loop
+loop:
+  %iv = phi i64 [ -20, %entry ], [ %iv.next, %loop ]
+  %iv.next = add nsw i64 %iv, 2
+  %narrow.iv = trunc i64 %iv to i32
+  %cmp = icmp sgt i32 1024, %narrow.iv
+  br i1 %cmp, label %loop, label %exit
+exit:
+  ret void
+}
+
 !0 = !{i32 0, i32 1000}