[ConstantFold] Fix comparison between special pointer constants

This code was assuming that the LHS would always be one of
GlobalVariable, BlockAddress or ConstantExpr. However, it can
also be a special constant like dso_local_equivalent or no_cfi.
Make sure this is handled gracefully.

Author: nikic

llvm/lib/IR/ConstantFold.cpp

@@ -1154,10 +1154,9 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2) {
                                 GV->getType()->getAddressSpace()))
         return ICmpInst::ICMP_UGT;
     }
-  } else {
+  } else if (auto *CE1 = dyn_cast<ConstantExpr>(V1)) {
     // Ok, the LHS is known to be a constantexpr.  The RHS can be any of a
     // constantexpr, a global, block address, or a simple constant.
-    ConstantExpr *CE1 = cast<ConstantExpr>(V1);
     Constant *CE1Op0 = CE1->getOperand(0);
 
     switch (CE1->getOpcode()) {

llvm/test/Transforms/InstSimplify/ConstProp/icmp-global.ll

@@ -298,3 +298,11 @@ bb:
   %cmp = icmp eq ptr blockaddress(@blockaddr_no_cfi, %bb), no_cfi @func
   ret i1 %cmp
 }
+
+define i1 @global_no_cfi_dso_local_equivalent() {
+; CHECK-LABEL: @global_no_cfi_dso_local_equivalent(
+; CHECK-NEXT:    ret i1 icmp eq (ptr dso_local_equivalent @func, ptr no_cfi @func)
+;
+  %cmp = icmp eq ptr dso_local_equivalent @func, no_cfi @func
+  ret i1 %cmp
+}