Merging r168921: into the 3.2 release branch.

Follow up to 168711: It's safe to base this analysis on the found compare, just return the value for the right predicate.

Thanks to Andy for catching this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_32@168974 91177308-0d34-0410-b5e6-96231b3b80d8

Author: 32bitmicro

lib/Analysis/ScalarEvolution.cpp

@@ -6149,10 +6149,9 @@ bool ScalarEvolution::isImpliedCond(ICmpInst::Predicate Pred,
   if (SimplifyICmpOperands(Pred, LHS, RHS))
     if (LHS == RHS)
       return CmpInst::isTrueWhenEqual(Pred);
-
-  // Canonicalize the found cond too.  We can't conclude a result from the
-  // simplified values.
-  SimplifyICmpOperands(FoundPred, FoundLHS, FoundRHS);
+  if (SimplifyICmpOperands(FoundPred, FoundLHS, FoundRHS))
+    if (FoundLHS == FoundRHS)
+      return CmpInst::isFalseWhenEqual(FoundPred);
 
   // Check to see if we can make the LHS or RHS match.
   if (LHS == FoundRHS || RHS == FoundLHS) {

test/Transforms/IndVarSimplify/eliminate-comparison.ll

@@ -160,3 +160,52 @@ unrolledend:                                      ; preds = %forcond38
 }
 
 declare void @llvm.trap() noreturn nounwind
+
+; In this case the second loop only has a single iteration, fold the header away
+; CHECK: @func_12
+; CHECK: %tmp5 = icmp slt i32 %__key6.0, 10
+; CHECK: br i1 true, label %noassert68, label %unrolledend
+define i32 @func_12() nounwind uwtable {
+entry:
+  br label %forcond
+
+forcond:                                          ; preds = %noassert, %entry
+  %__key6.0 = phi i32 [ 2, %entry ], [ %tmp37, %noassert ]
+  %tmp5 = icmp slt i32 %__key6.0, 10
+  br i1 %tmp5, label %noassert, label %forcond38.preheader
+
+forcond38.preheader:                              ; preds = %forcond
+  br label %forcond38
+
+noassert:                                         ; preds = %forbody
+  %tmp13 = sdiv i32 -32768, %__key6.0
+  %tmp2936 = shl i32 %tmp13, 24
+  %sext23 = shl i32 %tmp13, 24
+  %tmp32 = icmp eq i32 %tmp2936, %sext23
+  %tmp37 = add i32 %__key6.0, 1
+  br i1 %tmp32, label %forcond, label %assert33
+
+assert33:                                         ; preds = %noassert
+  tail call void @llvm.trap()
+  unreachable
+
+forcond38:                                        ; preds = %noassert68, %forcond38.preheader
+  %__key8.0 = phi i32 [ %tmp81, %noassert68 ], [ 2, %forcond38.preheader ]
+  %tmp46 = icmp slt i32 %__key8.0, 10
+  br i1 %tmp46, label %noassert68, label %unrolledend
+
+noassert68:                                       ; preds = %forbody39
+  %tmp57 = sdiv i32 -32768, %__key8.0
+  %sext34 = shl i32 %tmp57, 16
+  %sext21 = shl i32 %tmp57, 16
+  %tmp76 = icmp ne i32 %sext34, %sext21
+  %tmp81 = add i32 %__key8.0, 1
+  br i1 %tmp76, label %forcond38, label %assert77
+
+assert77:                                         ; preds = %noassert68
+  tail call void @llvm.trap()
+  unreachable
+
+unrolledend:                                      ; preds = %forcond38
+  ret i32 0
+}