1 files changed, 16 insertions, 48 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index fec51aa5ec6..2be03bd7f04 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1052,69 +1052,37 @@ Instruction *InstCombiner::FoldICmpCstShrCst(ICmpInst &I, Value *Op, Value *A,
   APInt AP1 = CI1->getValue();
   APInt AP2 = CI2->getValue();
 
-  if (!AP1) {
-    if (!AP2) {
-      // Both Constants are 0.
-      return getConstant(true);
-    }
-
-    if (cast<BinaryOperator>(Op)->isExact())
-      return getConstant(false);
-
-    if (AP2.isNegative()) {
-      // MSB is set, so a lshr with a large enough 'A' would be undefined.
-      return getConstant(false);
-    }
+  assert(AP2 != 0 && "Handled in InstSimplify");
+  assert(!AP2.isAllOnesValue() && "Handled in InstSimplify");
 
+  if (!AP1)
     // 'A' must be large enough to shift out the highest set bit.
     return getICmp(I.ICMP_UGT, A,
                    ConstantInt::get(A->getType(), AP2.logBase2()));
-  }
-
-  if (!AP2) {
-    // Shifting 0 by any value gives 0.
-    return getConstant(false);
-  }
 
-  bool IsAShr = isa<AShrOperator>(Op);
-  if (AP1 == AP2) {
-    if (AP1.isAllOnesValue() && IsAShr) {
-      // Arithmatic shift of -1 is always -1.
-      return getConstant(true);
-    }
+  if (AP1 == AP2)
     return getICmp(I.ICMP_EQ, A, ConstantInt::getNullValue(A->getType()));
-  }
-
-  bool IsNegative = false;
-  if (IsAShr) {
-    if (AP1.isNegative() != AP2.isNegative()) {
-      // Arithmetic shift will never change the sign.
-      return getConstant(false);
-    }
-    // Both the constants are negative, take their positive to calculate log.
-    if (AP1.isNegative()) {
-      if (AP1.slt(AP2))
-        // Right-shifting won't increase the magnitude.
-        return getConstant(false);
-      IsNegative = true;
-    }
-  }
 
-  if (!IsNegative && AP1.ugt(AP2))
-    // Right-shifting will not increase the value.
-    return getConstant(false);
+  bool IsAShr = isa<AShrOperator>(Op);
+  // If we are dealing with an arithmetic shift, both constants should agree in
+  // sign.  InstSimplify's SimplifyICmpInst range analysis is supposed to catch
+  // the cases when they disagree.
+  assert((!IsAShr || (AP1.isNegative() == AP2.isNegative() && AP1.sgt(AP2))) &&
+         "Handled in InstSimplify");
 
   // Get the distance between the highest bit that's set.
   int Shift;
-  if (IsNegative)
+  // Both the constants are negative, take their positive to calculate log.
+  if (IsAShr && AP1.isNegative())
     // Get the ones' complement of AP2 and AP1 when computing the distance.
     Shift = (~AP2).logBase2() - (~AP1).logBase2();
   else
     Shift = AP2.logBase2() - AP1.logBase2();
 
-  if (IsAShr ? AP1 == AP2.ashr(Shift) : AP1 == AP2.lshr(Shift))
-    return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift));
-
+  if (Shift > 0) {
+    if (IsAShr ? AP1 == AP2.ashr(Shift) : AP1 == AP2.lshr(Shift))
+      return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift));
+  }
   // Shifting const2 will never be equal to const1.
   return getConstant(false);
 }