[PATCH] D22441: Fix isShiftedInt and isShiftedUint for widths > 32.

[Justin Lebar via llvm-commits]

jlebar created this revision.
jlebar added a reviewer: rnk.
jlebar added subscribers: dylanmckay, llvm-commits.

Previously we were doing 1 << S.  "1" is an int, so this doesn't work
when S >= 32.

This patch also adds some static_asserts to these functions to ensure
that we don't hit UB by shifting left too much.

https://reviews.llvm.org/D22441

Files:
  include/llvm/Support/MathExtras.h
  unittests/Support/MathExtrasTest.cpp

Index: unittests/Support/MathExtrasTest.cpp
===================================================================
--- unittests/Support/MathExtrasTest.cpp
+++ unittests/Support/MathExtrasTest.cpp
@@ -388,4 +388,40 @@
   SaturatingMultiplyAddTestHelper<uint64_t>();
 }
 
+TEST(MathExtras, IsShiftedUInt) {
+  EXPECT_TRUE((isShiftedUInt<1, 0>(0)));
+  EXPECT_TRUE((isShiftedUInt<1, 0>(1)));
+  EXPECT_FALSE((isShiftedUInt<1, 0>(2)));
+  EXPECT_FALSE((isShiftedUInt<1, 0>(3)));
+  EXPECT_FALSE((isShiftedUInt<1, 0>(0x8000000000000000)));
+  EXPECT_TRUE((isShiftedUInt<1, 63>(0x8000000000000000)));
+  EXPECT_TRUE((isShiftedUInt<2, 62>(0xC000000000000000)));
+  EXPECT_FALSE((isShiftedUInt<2, 62>(0xE000000000000000)));
+
+  // 0x201 is ten bits long and has a 1 in the MSB and LSB.
+  EXPECT_TRUE((isShiftedUInt<10, 5>(uint64_t(0x201) << 5)));
+  EXPECT_FALSE((isShiftedUInt<10, 5>(uint64_t(0x201) << 4)));
+  EXPECT_FALSE((isShiftedUInt<10, 5>(uint64_t(0x201) << 6)));
+}
+
+TEST(MathExtras, IsShiftedInt) {
+  EXPECT_TRUE((isShiftedInt<1, 0>(0)));
+  EXPECT_TRUE((isShiftedInt<1, 0>(-1)));
+  EXPECT_FALSE((isShiftedInt<1, 0>(2)));
+  EXPECT_FALSE((isShiftedInt<1, 0>(3)));
+  EXPECT_FALSE((isShiftedInt<1, 0>(0x8000000000000000)));
+  EXPECT_TRUE((isShiftedInt<1, 63>(0x8000000000000000)));
+  EXPECT_TRUE((isShiftedInt<2, 62>(0xC000000000000000)));
+  EXPECT_FALSE((isShiftedInt<2, 62>(0xE000000000000000)));
+
+  // 0x201 is ten bits long and has a 1 in the MSB and LSB.
+  EXPECT_TRUE((isShiftedInt<11, 5>(int64_t(0x201) << 5)));
+  EXPECT_FALSE((isShiftedInt<11, 5>(int64_t(0x201) << 3)));
+  EXPECT_FALSE((isShiftedInt<11, 5>(int64_t(0x201) << 6)));
+  EXPECT_TRUE((isShiftedInt<11, 5>(-(int64_t(0x201) << 5))));
+  EXPECT_FALSE((isShiftedInt<11, 5>(-(int64_t(0x201) << 3))));
+  EXPECT_FALSE((isShiftedInt<11, 5>(-(int64_t(0x201) << 6))));
+
+  EXPECT_TRUE((isShiftedInt<6, 10>(-(int64_t(1) << 15))));
+  EXPECT_FALSE((isShiftedInt<6, 10>(int64_t(1) << 15)));
 }
Index: include/llvm/Support/MathExtras.h
===================================================================
--- include/llvm/Support/MathExtras.h
+++ include/llvm/Support/MathExtras.h
@@ -283,12 +283,16 @@
 ///                     left by S.
 template<unsigned N, unsigned S>
 inline bool isShiftedInt(int64_t x) {
-  return isInt<N+S>(x) && (x % (1<<S) == 0);
+  static_assert(
+      N > 0, "isShiftedInt<0> doesn't make sense (refers to a 0-bit number.");
+  static_assert(N + S <= 64, "isShiftedInt<N, S> with N + S > 64 is too wide.");
+  return isInt<N + S>(x) && (x % (UINT64_C(1) << S) == 0);
 }
 
 /// isUInt - Checks if an unsigned integer fits into the given bit width.
 template<unsigned N>
 inline bool isUInt(uint64_t x) {
+  static_assert(N > 0, "isUInt<0> doesn't make sense.");
   return N >= 64 || x < (UINT64_C(1)<<(N));
 }
 // Template specializations to get better code for common cases.
@@ -305,11 +309,16 @@
   return static_cast<uint32_t>(x) == x;
 }
 
-/// isShiftedUInt<N,S> - Checks if a unsigned integer is an N bit number shifted
-///                     left by S.
+/// Checks if a unsigned integer is an N bit number shifted left by S.
 template<unsigned N, unsigned S>
 inline bool isShiftedUInt(uint64_t x) {
-  return isUInt<N+S>(x) && (x % (1<<S) == 0);
+  static_assert(
+      N > 0, "isShiftedUInt<0> doesn't make sense (refers to a 0-bit number)");
+  static_assert(N + S <= 64,
+                "isShiftedUInt<N, S> with N + S > 64 is too wide.");
+  // Per the two static_asserts above, S must be strictly less than 64.  So
+  // 1 << S is not undefined behavior.
+  return isUInt<N + S>(x) && (x % (UINT64_C(1) << S) == 0);
 }
 
 /// Gets the maximum value for a N-bit unsigned integer.


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