Fix a bogus optimization: folding (slt (zext i1 A to i32), 1) -> (slt i1 A, true)

This cause a regression in InstCombine/JavaCompare, which was doing the right
thing on accident.  To handle the missed case, generalize the comparisons based
on masked bits a little bit to handle comparisons against the max value. For 
example, we can now xform (slt i32 (and X, 4), 4) -> (setne i32 (and X, 4), 4)




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53443 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 23 insertions, 16 deletions

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index e0e3f49be1..8cc7c05425 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -5230,7 +5230,7 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
   // See if we are doing a comparison between a constant and an instruction that
   // can be folded into the comparison.
   if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
-      Value *A, *B;
+    Value *A, *B;
     
     // (icmp ne/eq (sub A B) 0) -> (icmp ne/eq A, B)
     if (I.isEquality() && CI->isNullValue() &&
@@ -5396,6 +5396,8 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
           return ReplaceInstUsesWith(I, ConstantInt::getTrue());
         if (Min.sgt(RHSVal))
           return ReplaceInstUsesWith(I, ConstantInt::getFalse());
+        if (Max == RHSVal)  // A <s MAX -> A != MAX
+          return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1);
         break;
       case ICmpInst::ICMP_SGT: 
         if (Min.sgt(RHSVal))
@@ -6300,12 +6302,11 @@ Instruction *InstCombiner::visitICmpInstWithCastAndCast(ICmpInst &ICI) {
     //    %B = icmp ugt short %X, 1330 
     // because %A may have negative value. 
     //
-    // However, it is OK if SrcTy is bool (See cast-set.ll testcase)
-    // OR operation is EQ/NE.
-    if (isSignedExt == isSignedCmp || SrcTy == Type::Int1Ty || ICI.isEquality())
+    // However, we allow this when the compare is EQ/NE, because they are
+    // signless.
+    if (isSignedExt == isSignedCmp || ICI.isEquality())
       return new ICmpInst(ICI.getPredicate(), LHSCIOp, Res1);
-    else
-      return 0;
+    return 0;
   }
 
   // The re-extended constant changed so the constant cannot be represented 
@@ -6343,17 +6344,15 @@ Instruction *InstCombiner::visitICmpInstWithCastAndCast(ICmpInst &ICI) {
 
   // Finally, return the value computed.
   if (ICI.getPredicate() == ICmpInst::ICMP_ULT ||
-      ICI.getPredicate() == ICmpInst::ICMP_SLT) {
+      ICI.getPredicate() == ICmpInst::ICMP_SLT)
     return ReplaceInstUsesWith(ICI, Result);
-  } else {
-    assert((ICI.getPredicate()==ICmpInst::ICMP_UGT || 
-            ICI.getPredicate()==ICmpInst::ICMP_SGT) &&
-           "ICmp should be folded!");
-    if (Constant *CI = dyn_cast<Constant>(Result))
-      return ReplaceInstUsesWith(ICI, ConstantExpr::getNot(CI));
-    else
-      return BinaryOperator::CreateNot(Result);
-  }
+
+  assert((ICI.getPredicate()==ICmpInst::ICMP_UGT || 
+          ICI.getPredicate()==ICmpInst::ICMP_SGT) &&
+         "ICmp should be folded!");
+  if (Constant *CI = dyn_cast<Constant>(Result))
+    return ReplaceInstUsesWith(ICI, ConstantExpr::getNot(CI));
+  return BinaryOperator::CreateNot(Result);
 }
 
 Instruction *InstCombiner::visitShl(BinaryOperator &I) {
diff --git a/test/Transforms/InstCombine/2008-07-10-CastSextBool.ll b/test/Transforms/InstCombine/2008-07-10-CastSextBool.ll
new file mode 100644
index 0000000000..f5efefb0a0
--- /dev/null
+++ b/test/Transforms/InstCombine/2008-07-10-CastSextBool.ll
@@ -0,0 +1,8 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {%C = xor i1 %A, true}
+; PR2539
+
+define i1 @test(i1 %A) {
+	%B = zext i1 %A to i32
+	%C = icmp slt i32 %B, 1
+	ret i1 %C
+}