[llvm] r275720 - Add assertions checking SignExtend{32, 64}'s bit width.

[Justin Lebar via llvm-commits]

Author: jlebar
Date: Sun Jul 17 13:19:23 2016
New Revision: 275720

URL: http://llvm.org/viewvc/llvm-project?rev=275720&view=rev
Log:
Add assertions checking SignExtend{32,64}'s bit width.

Summary:
The bit width must be greater than zero, otherwise we shift by the
integer's width, which is UB.  Also (more obviously) the width must be
less than or equal to the integer's width, otherwise we shift by a
negative number, which is also UB.

Reviewers: rnk

Subscribers: llvm-commits, dylanmckay

Differential Revision: https://reviews.llvm.org/D22442

Modified:
    llvm/trunk/include/llvm/Support/MathExtras.h

Modified: llvm/trunk/include/llvm/Support/MathExtras.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/MathExtras.h?rev=275720&r1=275719&r2=275720&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/MathExtras.h (original)
+++ llvm/trunk/include/llvm/Support/MathExtras.h Sun Jul 17 13:19:23 2016
@@ -672,27 +672,35 @@ inline uint64_t OffsetToAlignment(uint64
   return alignTo(Value, Align) - Value;
 }
 
-/// SignExtend32 - Sign extend B-bit number x to 32-bit int.
-/// Usage int32_t r = SignExtend32<5>(x);
-template <unsigned B> inline int32_t SignExtend32(uint32_t x) {
-  return int32_t(x << (32 - B)) >> (32 - B);
+/// Sign-extend the number in the bottom B bits of X to a 32-bit integer.
+/// Requires 0 < B <= 32.
+template <unsigned B> inline int32_t SignExtend32(uint32_t X) {
+  static_assert(B > 0, "Bit width can't be 0.");
+  static_assert(B <= 32, "Bit width out of range.");
+  return int32_t(X << (32 - B)) >> (32 - B);
 }
 
-/// \brief Sign extend number in the bottom B bits of X to a 32-bit int.
-/// Requires 0 < B <= 32.
+/// Sign-extend the number in the bottom B bits of X to a 32-bit integer.
+/// Requires 0 < B < 32.
 inline int32_t SignExtend32(uint32_t X, unsigned B) {
+  assert(B > 0 && "Bit width can't be 0.");
+  assert(B <= 32 && "Bit width out of range.");
   return int32_t(X << (32 - B)) >> (32 - B);
 }
 
-/// SignExtend64 - Sign extend B-bit number x to 64-bit int.
-/// Usage int64_t r = SignExtend64<5>(x);
+/// Sign-extend the number in the bottom B bits of X to a 64-bit integer.
+/// Requires 0 < B < 64.
 template <unsigned B> inline int64_t SignExtend64(uint64_t x) {
+  static_assert(B > 0, "Bit width can't be 0.");
+  static_assert(B <= 64, "Bit width out of range.");
   return int64_t(x << (64 - B)) >> (64 - B);
 }
 
-/// \brief Sign extend number in the bottom B bits of X to a 64-bit int.
-/// Requires 0 < B <= 64.
+/// Sign-extend the number in the bottom B bits of X to a 64-bit integer.
+/// Requires 0 < B < 64.
 inline int64_t SignExtend64(uint64_t X, unsigned B) {
+  assert(B > 0 && "Bit width can't be 0.");
+  assert(B <= 64 && "Bit width out of range.");
   return int64_t(X << (64 - B)) >> (64 - B);
 }