forked from OSchip/llvm-project
5bf0023b0d
Unlike what I claimed in my previous commit. The caching is actually not NFC on PHIs. When we put a big enough max depth, we end up simulating loops. The cache is effectively cutting the simulation short and we get less information as a result. E.g., ``` v0 = G_CONSTANT i8 0xC0 jump v1 = G_PHI i8 v0, v2 v2 = G_LSHR i8 v1, 1 ``` Let say we want the known bits of v1. - With cache: Set v1 cache to we know nothing v1 is v0 & v2 v0 gives us 0xC0 v2 gives us known bits of v1 >> 1 v1 is in the cache => v1 is 0, thus v2 is 0x80 Finally v1 is v0 & v2 => 0x80 - Without cache and enough depth to do two iteration of the loop: v1 is v0 & v2 v0 gives us 0xC0 v2 gives us known bits of v1 >> 1 v1 is v0 & v2 v0 is 0xC0 v2 is v1 >> 1 Reach the max depth for v1... unwinding v1 is know nothing v2 is 0x80 v0 is 0xC0 v1 is 0x80 v2 is 0xC0 v0 is 0xC0 v1 is 0xC0 Thus now v1 is 0xC0 instead of 0x80. I've added a unittest demonstrating that. NFC |
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| .. | ||
| CMakeLists.txt | ||
| CSETest.cpp | ||
| ConstantFoldingTest.cpp | ||
| GISelMITest.cpp | ||
| GISelMITest.h | ||
| KnownBitsTest.cpp | ||
| LegalizerHelperTest.cpp | ||
| LegalizerInfoTest.cpp | ||
| LegalizerTest.cpp | ||
| MachineIRBuilderTest.cpp | ||
| PatternMatchTest.cpp | ||