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Marge Bot pushed to branch master at <a href="https://gitlab.haskell.org/ghc/ghc" style="color: #1068bf;">Glasgow Haskell Compiler / GHC</a>
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Commits:
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<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/f058e3672b969f301b6b1637f8ab081654ec947a" style="color: #1068bf;">f058e367</a></strong>
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<span> by Ben Gamari </span> <i> at 2023-01-18T22:25:27-05:00 </i>
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<pre class="commit-message" style='white-space: pre-wrap; display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: #fafafa; border-radius: 2px; margin: 0; padding: 8px 12px; border: 1px solid #dbdbdb;'>nativeGen/X86: MFENCE is unnecessary for release semantics
In #22764 a user noticed that a program implementing a simple atomic
counter via an STRef regressed significantly due to the introduction of
necessary atomic operations in the MutVar# primops (#22468). This
regression was caused by a bug in the NCG, which emitted an unnecessary
MFENCE instruction for a release-ordered atomic write. MFENCE is rather
only needed to achieve sequentially consistent ordering.
Fixes #22764.
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1 changed file:
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<a href="#2bae5947e9412f6deebf4db7dcb89d780913130f" style="color: #1068bf;">
compiler/GHC/CmmToAsm/X86/CodeGen.hs
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Changes:
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<a href="https://gitlab.haskell.org/ghc/ghc/-/commit/f058e3672b969f301b6b1637f8ab081654ec947a#2bae5947e9412f6deebf4db7dcb89d780913130f" style="color: #1068bf;"><strong style="font-weight: bold;">compiler/GHC/CmmToAsm/X86/CodeGen.hs</strong></a>
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<td class="diff-line-num unfold js-unfold old_line" data-linenumber="3936" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">...</td>
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<td class="line_content match" style="color: rgba(0,0,0,0.3); padding: inherit;" bgcolor="#fafafa">@@ -3936,7 +3936,7 @@ genAtomicWrite width mord addr val = do</td>
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<td class="old_line diff-line-num" data-linenumber="3936" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
3936
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<td class="new_line diff-line-num" data-linenumber="3936" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
3936
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC3936" class="line" lang="haskell"> <span class="n" style="color: #333;">code</span> <span class="o" style="font-weight: 600;"><-</span> <span class="n" style="color: #333;">assignMem_IntCode</span> <span class="p">(</span><span class="n" style="color: #333;">intFormat</span> <span class="n" style="color: #333;">width</span><span class="p">)</span> <span class="n" style="color: #333;">addr</span> <span class="n" style="color: #333;">val</span></span>
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<td class="old_line diff-line-num" data-linenumber="3937" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
3937
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<td class="new_line diff-line-num" data-linenumber="3937" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
3937
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC3937" class="line" lang="haskell"> <span class="kr" style="font-weight: 600;">let</span> <span class="n" style="color: #333;">needs_fence</span> <span class="o" style="font-weight: 600;">=</span> <span class="kr" style="font-weight: 600;">case</span> <span class="n" style="color: #333;">mord</span> <span class="kr" style="font-weight: 600;">of</span></span>
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<td class="old_line diff-line-num" data-linenumber="3938" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
3938
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<td class="new_line diff-line-num" data-linenumber="3938" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
3938
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC3938" class="line" lang="haskell"> <span class="kt" style="color: #458; font-weight: 600;">MemOrderSeqCst</span> <span class="o" style="font-weight: 600;">-></span> <span class="kt" style="color: #458; font-weight: 600;">True</span></span>
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<td class="old_line diff-line-num old" data-linenumber="3939" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #fac5cd; border-right-style: solid; padding: inherit;" align="right" bgcolor="#f9d7dc">
3939
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<td class="new_line diff-line-num old" data-linenumber="3939" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #fac5cd; border-right-style: solid; padding: inherit;" align="right" bgcolor="#f9d7dc">
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<td class="line_content old" style="padding: inherit;" bgcolor="#fbe9eb"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>-<span id="LC3939" class="line" lang="haskell"> <span class="kt" style="color: #458; font-weight: 600;">MemOrderRelease</span> <span class="o" style="font-weight: 600;">-></span> <span class="kt" style="color: #458; font-weight: 600;"><span class="idiff left right deletion" style="background-color: #fac5cd;">Tru</span>e</span></span>
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<td class="old_line diff-line-num new" data-linenumber="3940" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
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<td class="new_line diff-line-num new" data-linenumber="3939" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
3939
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC3939" class="line" lang="haskell"> <span class="kt" style="color: #458; font-weight: 600;">MemOrderRelease</span> <span class="o" style="font-weight: 600;">-></span> <span class="kt" style="color: #458; font-weight: 600;"><span class="idiff left right addition" style="background-color: #c7f0d2;">Fals</span>e</span></span>
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3940
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<td class="new_line diff-line-num" data-linenumber="3940" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
3940
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC3940" class="line" lang="haskell"> <span class="kt" style="color: #458; font-weight: 600;">MemOrderAcquire</span> <span class="o" style="font-weight: 600;">-></span> <span class="n" style="color: #333;">pprPanic</span> <span class="s" style="color: #d14;">"genAtomicWrite: acquire ordering on write"</span> <span class="n" style="color: #333;">empty</span></span>
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<td class="old_line diff-line-num" data-linenumber="3941" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
3941
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<td class="new_line diff-line-num" data-linenumber="3941" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
3941
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC3941" class="line" lang="haskell"> <span class="kt" style="color: #458; font-weight: 600;">MemOrderRelaxed</span> <span class="o" style="font-weight: 600;">-></span> <span class="kt" style="color: #458; font-weight: 600;">False</span></span>
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<td class="old_line diff-line-num" data-linenumber="3942" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
3942
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<td class="new_line diff-line-num" data-linenumber="3942" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
3942
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC3942" class="line" lang="haskell"> <span class="n" style="color: #333;">return</span> <span class="o" style="font-weight: 600;">$</span> <span class="kr" style="font-weight: 600;">if</span> <span class="n" style="color: #333;">needs_fence</span> <span class="kr" style="font-weight: 600;">then</span> <span class="n" style="color: #333;">code</span> <span class="p">`</span><span class="n" style="color: #333;">snocOL</span><span class="p">`</span> <span class="kt" style="color: #458; font-weight: 600;">MFENCE</span> <span class="kr" style="font-weight: 600;">else</span> <span class="n" style="color: #333;">code</span></span>
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