From 2742f3de37e5856e2ab291248d7217332f51c912 Mon Sep 17 00:00:00 2001
From: Leonard Hecker <lhecker@microsoft.com>
Date: Wed, 21 Feb 2024 18:54:35 +0100
Subject: [PATCH] Fix an apparent x86 miscompilation on MSVC 19.38 (#16742)

There's an apparent miscompilation of `dynamic_bitset` on x86 with
MSVC 19.38, where the following code:
```cpp
dynamic_bitset<uint64_t> bits(80 * 24, 0);
bits.set(0, 3 * 80, true);
```

is expected to set the first 3.75 blocks to 1 which should produce
the following blocks:
```
0xffffffffffffffff
0xffffffffffffffff
0xffffffffffffffff
0x0000ffffffffffff
```

but it actually produces:
```
0xffffffffffffffff
0x00000000ffffffff
0xffffffffffffffff
0x0000ffffffffffff
```

The weird thing here is that this only happens if `til::bitmap`
uses a `dynamic_bitset<uint64_t>`. As soon as it uses `<uint32_t>`
any other instantiation of `<uint64_t>` is magically fixed.

Conclusion: Use `size_t` until we know what's going on.
Last known good CL version: 14.37.32822
Current broken CL version: 14.38.33130

## Validation Steps Performed

The following test completes successfully again:
```cpp
til::bitmap map{ { 80, 24 } };
map.translate({ 0, 3 }, true);
VERIFY_ARE_EQUAL(3u, map.runs().size());
```

(cherry picked from commit d3ec47a7fc3d4d5d50d2b66bae5f1a872ce3322d)
Service-Card-Id: 91894072
Service-Version: 1.18
---
 src/inc/til/bitmap.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/inc/til/bitmap.h b/src/inc/til/bitmap.h
index 38213500477..3934af878cc 100644
--- a/src/inc/til/bitmap.h
+++ b/src/inc/til/bitmap.h
@@ -23,7 +23,7 @@ namespace til // Terminal Implementation Library. Also: "Today I Learned"
             using pointer = const til::rect*;
             using reference = const til::rect&;
 
-            _bitmap_const_iterator(const dynamic_bitset<unsigned long long, Allocator>& values, til::rect rc, ptrdiff_t pos) :
+            _bitmap_const_iterator(const dynamic_bitset<size_t, Allocator>& values, til::rect rc, ptrdiff_t pos) :
                 _values(values),
                 _rc(rc),
                 _pos(pos),
@@ -77,7 +77,7 @@ namespace til // Terminal Implementation Library. Also: "Today I Learned"
             }
 
         private:
-            const dynamic_bitset<unsigned long long, Allocator>& _values;
+            const dynamic_bitset<size_t, Allocator>& _values;
             const til::rect _rc;
             size_t _pos;
             size_t _nextPos;
@@ -133,7 +133,7 @@ namespace til // Terminal Implementation Library. Also: "Today I Learned"
             }
         };
 
-        template<typename Allocator = std::allocator<unsigned long long>>
+        template<typename Allocator = std::allocator<size_t>>
         class bitmap
         {
         public:
@@ -538,7 +538,7 @@ namespace til // Terminal Implementation Library. Also: "Today I Learned"
             allocator_type _alloc;
             til::size _sz;
             til::rect _rc;
-            dynamic_bitset<unsigned long long, allocator_type> _bits;
+            dynamic_bitset<size_t, allocator_type> _bits;
 
             mutable std::optional<std::vector<til::rect, run_allocator_type>> _runs;
 
@@ -553,7 +553,7 @@ namespace til // Terminal Implementation Library. Also: "Today I Learned"
 
     namespace pmr
     {
-        using bitmap = ::til::details::bitmap<std::pmr::polymorphic_allocator<unsigned long long>>;
+        using bitmap = ::til::details::bitmap<std::pmr::polymorphic_allocator<size_t>>;
     }
 }