Index: lib/Transforms/Scalar/Reassociate.cpp
===================================================================
--- lib/Transforms/Scalar/Reassociate.cpp
+++ lib/Transforms/Scalar/Reassociate.cpp
@@ -1520,8 +1520,8 @@
       if (ConstantInt *CI = dyn_cast<ConstantInt>(Factor)) {
         if (CI->isNegative() && !CI->isMinValue(true)) {
           Factor = ConstantInt::get(CI->getContext(), -CI->getValue());
-          assert(!Duplicates.count(Factor) &&
-                 "Shouldn't have two constant factors, missed a canonicalize");
+          if (!Duplicates.insert(Factor).second)
+            continue;
           unsigned Occ = ++FactorOccurrences[Factor];
           if (Occ > MaxOcc) {
             MaxOcc = Occ;
@@ -1533,8 +1533,8 @@
           APFloat F(CF->getValueAPF());
           F.changeSign();
           Factor = ConstantFP::get(CF->getContext(), F);
-          assert(!Duplicates.count(Factor) &&
-                 "Shouldn't have two constant factors, missed a canonicalize");
+          if (!Duplicates.insert(Factor).second)
+            continue;
           unsigned Occ = ++FactorOccurrences[Factor];
           if (Occ > MaxOcc) {
             MaxOcc = Occ;
Index: test/Transforms/Reassociate/basictest.ll
===================================================================
--- test/Transforms/Reassociate/basictest.ll
+++ test/Transforms/Reassociate/basictest.ll
@@ -222,3 +222,19 @@
 ; CHECK-LABEL: @test15
 ; CHECK: and i1 %A, %B
 }
+
+; PR30256 - Just make sure we don't hit an assert.
+define i64 @test16(i1 %cmp, i64 %a, i64 %b) {
+entry:
+  %shl = shl i64 %a, 1
+  %shl.neg = sub i64 0, %shl
+  br i1 %cmp, label %if.then, label %if.end
+
+if.then:                                          ; preds = %entry
+  %add1 = add i64 %shl.neg, %shl.neg
+  %add2 = add i64 %add1, %b
+  ret i64 %add2
+
+if.end:                                           ; preds = %entry
+  ret i64 0
+}