[APInt] Allow self-assignment with libstdc++

[vitalybuka]

Summary

http://lab.llvm.org:8011/builders/llvm-clang-x86_64-expensive-checks-ubuntu/builds/8256/steps/test-check-all/logs/FAIL%3A%20LLVM%3A%3Athinlto-function-summary-paramaccess.ll

[vitalybuka]

rebase

[craig.topper]

llvm/unittests/ADT/APIntTest.cpp

1785–1786

This comment needs to be updated

[vitalybuka]

I would prefer to remove if def completly and always compile with if (this == &that)
Original patch justified removing of (this == &that) to save 4k. I don't think it's worth it.
However if want to remove this from release maybe we should do the following, as EXPENSIVE_CHECKS is the one who triggers std::shuffle in llvm::sort?

#ifdef EXPENSIVE_CHECKS
   if (this == &that)
      return *this;
#endif

[vitalybuka]

update comment

[RKSimon]

In D86053#2225049, @vitalybuka wrote:

I would prefer to remove if def completly and always compile with if (this == &that)
Original patch justified removing of (this == &that) to save 4k. I don't think it's worth it.
However if want to remove this from release maybe we should do the following, as EXPENSIVE_CHECKS is the one who triggers std::shuffle in llvm::sort?

#ifdef EXPENSIVE_CHECKS
   if (this == &that)
      return *this;
#endif

This makes sense to me - we keep the codesize savings on main builds and we have a better chance of seeing self-moves on windows bots.

[vitalybuka]

Use EXPENSIVE_CHECKS

[RKSimon]

LGTM

llvm/include/llvm/ADT/APInt.h

APInt &operator=(const APInt &RHS) {
     }
 
     AssignSlowCase(RHS);
     return *this;
   }
 
   /// Move assignment operator.
   APInt &operator=(APInt &&that) {
-#ifdef _MSC_VER
-    // The MSVC std::shuffle implementation still does self-assignment.
+#ifdef EXPENSIVE_CHECKS
+    // Some std::shuffle implementations still do self-assignment.
     if (this == &that)
       return *this;
 #endif
     assert(this != &that && "Self-move not supported");
     if (!isSingleWord())
       delete[] U.pVal;
 
     // Use memcpy so that type based alias analysis sees both VAL and pVal

llvm/unittests/ADT/APIntTest.cpp

for (int I = 1; I < N - 1; ++I) {
       EXPECT_TRUE(MaskVal.isShiftedMask());
     }
     for (int I = 1; I < N; ++I) {
       APInt MaskVal = APInt::getHighBitsSet(N, I);
       EXPECT_TRUE(MaskVal.isShiftedMask());
     }
   }
 }
 
-// Test that self-move works, but only when we're using MSVC.
-#if defined(_MSC_VER)
+// Test that self-move works with EXPENSIVE_CHECKS. It calls std::shuffle which
+// does self-move on some platforms.
+#ifdef EXPENSIVE_CHECKS
 #if defined(__clang__)
 // Disable the pragma warning from versions of Clang without -Wself-move
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wunknown-pragmas"
 // Disable the warning that triggers on exactly what is being tested.
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wself-move"
 #endif
TEST(APIntTest, SelfMoveAssignment) {
   EXPECT_EQ(2u, Y.getNumWords());
   EXPECT_EQ(0xdeadbeefdeadbeefULL, Raw[0]);
   EXPECT_EQ(0xdeadbeefdeadbeefULL, Raw[1]);
 }
 #if defined(__clang__)
 #pragma clang diagnostic pop
 #pragma clang diagnostic pop
 #endif
-#endif // _MSC_VER
+#endif // EXPENSIVE_CHECKS
 
 TEST(APIntTest, byteSwap) {
   EXPECT_EQ(0x00000000, APInt(16, 0x0000).byteSwap());
   EXPECT_EQ(0x0000010f, APInt(16, 0x0f01).byteSwap());
   EXPECT_EQ(0x00ff8000, APInt(24, 0x0080ff).byteSwap());
   EXPECT_EQ(0x117700ff, APInt(32, 0xff007711).byteSwap());
   EXPECT_EQ(0x228811aaffULL, APInt(40, 0xffaa118822ULL).byteSwap());
   EXPECT_EQ(0x050403020100ULL, APInt(48, 0x000102030405ULL).byteSwap());