[APInt] Add APInt::extractBits() method to extract APInt subrange (reapplied)
The current pattern for extract bits in range is typically:
Mask.lshr(BitOffset).trunc(SubSizeInBits);
Which can be particularly slow for large APInts (MaskSizeInBits > 64) as they require the allocation of memory for the temporary variable.
This is another of the compile time issues identified in PR32037 (see also D30265).
This patch adds the APInt::extractBits() helper method which avoids the temporary memory allocation.
Differential Revision: https://reviews.llvm.org/D30336
llvm-svn: 296272
diff --git a/llvm/unittests/ADT/APIntTest.cpp b/llvm/unittests/ADT/APIntTest.cpp
index 39a88cd..30da181 100644
--- a/llvm/unittests/ADT/APIntTest.cpp
+++ b/llvm/unittests/ADT/APIntTest.cpp
@@ -1505,3 +1505,19 @@
}
}
}
+
+TEST(APIntTest, extractBits) {
+ APInt i32(32, 0x1234567);
+ EXPECT_EQ(0x3456, i32.extractBits(16, 4));
+
+ APInt i257(257, 0xFFFFFFFFFF0000FFull, true);
+ EXPECT_EQ(0xFFu, i257.extractBits(16, 0));
+ EXPECT_EQ((0xFFu >> 1), i257.extractBits(16, 1));
+ EXPECT_EQ(-1, i257.extractBits(32, 64).getSExtValue());
+ EXPECT_EQ(-1, i257.extractBits(128, 128).getSExtValue());
+ EXPECT_EQ(-1, i257.extractBits(66, 191).getSExtValue());
+ EXPECT_EQ(static_cast<int64_t>(0xFFFFFFFFFF80007Full),
+ i257.extractBits(128, 1).getSExtValue());
+ EXPECT_EQ(static_cast<int64_t>(0xFFFFFFFFFF80007Full),
+ i257.extractBits(129, 1).getSExtValue());
+}