Use pragmas to work around MSVC x86_32 debug miscompile bug
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
NOTE from amaiorano@ : applied this LLVM patch (without the unittest) to SwiftShader.
Bug: b/173512119
Change-Id: If036f61386b51f9b4a20427812b4ac92d901244d
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/50469
Tested-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/third_party/llvm-10.0/llvm/lib/CodeGen/GlobalISel/LegalityPredicates.cpp b/third_party/llvm-10.0/llvm/lib/CodeGen/GlobalISel/LegalityPredicates.cpp
index 601d50e..f0f8c2d 100644
--- a/third_party/llvm-10.0/llvm/lib/CodeGen/GlobalISel/LegalityPredicates.cpp
+++ b/third_party/llvm-10.0/llvm/lib/CodeGen/GlobalISel/LegalityPredicates.cpp
@@ -10,6 +10,17 @@
//
//===----------------------------------------------------------------------===//
+// Enable 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;
