Fix PR13704

- The increment needs to be signed value to preserve the original value when
  its data type is larger than 64-bit integer.

llvm-svn: 162766

clang/lib/CodeGen/CGExprScalar.cpp

@@ -1306,7 +1306,7 @@ ScalarExprEmitter::EmitScalarPrePostIncDec(const UnaryOperator *E, LValue LV,
   // Most common case by far: integer increment.
   } else if (type->isIntegerType()) {
 
-    llvm::Value *amt = llvm::ConstantInt::get(value->getType(), amount);
+    llvm::Value *amt = llvm::ConstantInt::get(value->getType(), amount, true);
 
     // Note that signed integer inc/dec with width less than int can't
     // overflow because of promotion rules; we're just eliding a few steps here.

clang/test/CodeGen/pr13704.c

@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 %s -emit-llvm -o - | FileCheck %s
+extern void foo(__int128);
+
+void bar() {
+  __int128 x = 2;
+  x--;
+  foo(x);
+// CHECK: add nsw i128 %0, -1
+}