[Clang][CodeGen] Check isUnderlyingBasePointerConstantNull in emitPointerArithmetic

Author: dtcxzyw

clang/lib/CodeGen/CGExprScalar.cpp

@@ -4238,7 +4238,8 @@ static Value *emitPointerArithmetic(CodeGenFunction &CGF,
   else
     elemTy = CGF.ConvertTypeForMem(elementType);
 
-  if (CGF.getLangOpts().PointerOverflowDefined)
+  if (CGF.getLangOpts().PointerOverflowDefined ||
+      CGF.isUnderlyingBasePointerConstantNull(pointerOperand))
     return CGF.Builder.CreateGEP(elemTy, pointer, index, "add.ptr");
 
   return CGF.EmitCheckedInBoundsGEP(

clang/test/CodeGen/catch-nullptr-and-nonzero-offset.c

@@ -431,6 +431,18 @@ char *void_ptr(void *base, unsigned long offset) {
   return base + offset;
 }
 
+int *constant_null_add(long offset) {
+  // CHECK: define{{.*}} ptr @constant_null_add(i64 noundef %[[OFFSET:.*]])
+  // CHECK-NEXT: [[ENTRY:.*]]:
+  // CHECK-NEXT:   %[[OFFSET_ADDR:.*]] = alloca i64, align 8
+  // CHECK-NEXT:   store i64 %[[OFFSET]], ptr %[[OFFSET_ADDR]], align 8
+  // CHECK-NEXT:   %[[OFFSET_RELOADED:.*]] = load i64, ptr %[[OFFSET_ADDR]], align 8
+  // CHECK-NEXT:   %[[ADD_PTR:.*]] = getelementptr i32, ptr null, i64 %[[OFFSET_RELOADED]]
+  // CHECK-NEXT:   ret ptr %[[ADD_PTR]]
+#line 1800
+  return (int *)0 + offset;
+}
+
 #ifdef __cplusplus
 }
 #endif