Make constant evaluation for pointer comparisons work correctly for s…

…ome uncommon cases. <rdar://problem/10962435>.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@154794 91177308-0d34-0410-b5e6-96231b3b80d8

lib/AST/ExprConstant.cpp

@@ -5088,14 +5088,26 @@ bool IntExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
         }
       }
 
+      // The comparison here must be unsigned, and performed with the same
+      // width as the pointer.
+      // FIXME: Knowing the base is the same for the LHS and RHS isn't enough
+      // for relational operators.
+      unsigned PtrSize = Info.Ctx.getTypeSize(LHSTy);
+      uint64_t CompareLHS = LHSOffset.getQuantity();
+      uint64_t CompareRHS = RHSOffset.getQuantity();
+      assert(PtrSize <= 64 && "Unexpected pointer width");
+      uint64_t Mask = ~0ULL >> (64 - PtrSize);
+      CompareLHS &= Mask;
+      CompareRHS &= Mask;
+
       switch (E->getOpcode()) {
       default: llvm_unreachable("missing comparison operator");
-      case BO_LT: return Success(LHSOffset < RHSOffset, E);
-      case BO_GT: return Success(LHSOffset > RHSOffset, E);
-      case BO_LE: return Success(LHSOffset <= RHSOffset, E);
-      case BO_GE: return Success(LHSOffset >= RHSOffset, E);
-      case BO_EQ: return Success(LHSOffset == RHSOffset, E);
-      case BO_NE: return Success(LHSOffset != RHSOffset, E);
+      case BO_LT: return Success(CompareLHS < CompareRHS, E);
+      case BO_GT: return Success(CompareLHS > CompareRHS, E);
+      case BO_LE: return Success(CompareLHS <= CompareRHS, E);
+      case BO_GE: return Success(CompareLHS >= CompareRHS, E);
+      case BO_EQ: return Success(CompareLHS == CompareRHS, E);
+      case BO_NE: return Success(CompareLHS != CompareRHS, E);
       }
     }
   }

test/Sema/const-eval-64.c

@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -triple x86_64-linux %s
+
+#define EVAL_EXPR(testno, expr) int test##testno = sizeof(struct{char qq[expr];});
+
+// <rdar://problem/10962435>
+EVAL_EXPR(1, ((char*)-1LL) + 1 == 0 ? 1 : -1)
+EVAL_EXPR(2, ((char*)-1LL) + 1 < (char*) -1 ? 1 : -1)

test/Sema/const-eval.c

@@ -121,3 +121,7 @@ EVAL_EXPR(43, varfloat && constfloat) // expected-error {{must have a constant s
 // <rdar://problem/11205586>
 // (Make sure we continue to reject this.)
 EVAL_EXPR(44, "x"[0]); // expected-error {{variable length array}}
+
+// <rdar://problem/10962435>
+EVAL_EXPR(45, ((char*)-1) + 1 == 0 ? 1 : -1)
+EVAL_EXPR(46, ((char*)-1) + 1 < (char*) -1 ? 1 : -1)