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Use pragmas to work around MSVC x86_32 debug miscompile bug

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Halide users reported this here: https://llvm.org/pr46176
I reported the issue to MSVC here:
https://developercommunity.visualstudio.com/content/problem/1179643/msvc-copies-overaligned-non-trivially-copyable-par.html

This codepath is apparently not covered by LLVM's unit tests, so I added
coverage in a unit test.

If we want to support this configuration going forward, it means that is
in general not safe to pass a SmallVector<T, N> by value if alignof(T)
is greater than 4. This doesn't appear to come up often because passing
a SmallVector by value is inefficient and not idiomatic: it copies the
inline storage. In this case, the SmallVector<LLT,4> is captured by
value by a lambda, and the lambda is passed by value into std::function,
and that's how we hit the bug.

Differential Revision: https://reviews.llvm.org/D87475
This commit is contained in:
Reid Kleckner 2020-09-10 11:23:42 -07:00
parent 710443d7ab
commit e88b0fafb4
2 changed files with 21 additions and 0 deletions
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11
lib/CodeGen/GlobalISel/LegalityPredicates.cpp
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@ -10,6 +10,17 @@
//
//===----------------------------------------------------------------------===//
// Disable optimizations to work around MSVC debug mode bug in 32-bit:
// https://developercommunity.visualstudio.com/content/problem/1179643/msvc-copies-overaligned-non-trivially-copyable-par.html
// FIXME: Remove this when the issue is closed.
#if defined(_MSC_VER) && !defined(__clang__) && defined(_M_IX86)
// We have to disable runtime checks in order to enable optimizations. This is
// done for the entire file because the problem is actually observed in STL
// template functions.
#pragma runtime_checks("", off)
#pragma optimize("gs", on)
#endif
#include "llvm/CodeGen/GlobalISel/LegalizerInfo.h"
using namespace llvm;

10
unittests/CodeGen/GlobalISel/LegalizerInfoTest.cpp
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@ -406,3 +406,13 @@ TEST(LegalizerInfoTest, MMOAlignment) {
32, 8, AtomicOrdering::NotAtomic }));
}
}
// This code sequence doesn't do anything, but it covers a previously uncovered
// codepath that used to crash in MSVC x86_32 debug mode.
TEST(LegalizerInfoTest, MSVCDebugMiscompile) {
const LLT S1 = LLT::scalar(1);
const LLT P0 = LLT::pointer(0, 32);
LegalizerInfo LI;
auto Builder = LI.getActionDefinitionsBuilder(TargetOpcode::G_PTRTOINT);
(void)Builder.legalForCartesianProduct({S1}, {P0});
}