'RE: [PATCH] RE: [cfe-dev] missing return statement for non-void functions in C++'

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List:       cfe-commits
Subject:    RE: [PATCH] RE: [cfe-dev] missing return statement for non-void functions in C++
From:       Sjoerd Meijer via cfe-commits <cfe-commits () lists ! llvm ! org>
Date:       2015-08-17 12:33:51
Message-ID: 1C23526A7C42DB45BBF55B662C7C530E4E654C7B87 () BUNGLE ! Emea ! Arm ! com
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Agreed, let's get that right first.
The attached patch causes the program to trap for all optimizations levels, except \
when optimizing for size.

Sjoerd.

From: dosreis@gmail.com [mailto:dosreis@gmail.com] On Behalf Of Gabriel Dos Reis
Sent: 13 August 2015 21:51
To: Richard Smith
Cc: Sjoerd Meijer; Marshall Clow; cfe-commits
Subject: Re: [PATCH] RE: [cfe-dev] missing return statement for non-void functions in \
C++

Please make such programs crash early and often.  They are a nightmare to maintain.  \
Make them blow in the face of the original authors; not after they are gone.

-- Gaby


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<p class="MsoNormal"><span \
style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D">Agreed, \
let's get that right first.<o:p></o:p></span></p> <p class="MsoNormal"><span \
style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D">The \
attached patch causes the program to trap for all optimizations levels, except when \
optimizing for size.<o:p></o:p></span></p> <p class="MsoNormal"><span \
style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D"><o:p>&nbsp;</o:p></span></p>
 <p class="MsoNormal"><span \
style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D">Sjoerd.<o:p></o:p></span></p>
 <p class="MsoNormal"><span \
style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D"><o:p>&nbsp;</o:p></span></p>
 <p class="MsoNormal"><b><span lang="EN-US" \
style="font-size:10.0pt;font-family:&quot;Tahoma&quot;,&quot;sans-serif&quot;">From:</span></b><span \
lang="EN-US" style="font-size:10.0pt;font-family:&quot;Tahoma&quot;,&quot;sans-serif&quot;"> \
dosreis@gmail.com [mailto:dosreis@gmail.com] <b>On Behalf Of </b>Gabriel Dos Reis<br>
<b>Sent:</b> 13 August 2015 21:51<br>
<b>To:</b> Richard Smith<br>
<b>Cc:</b> Sjoerd Meijer; Marshall Clow; cfe-commits<br>
<b>Subject:</b> Re: [PATCH] RE: [cfe-dev] missing return statement for non-void \
functions in C&#43;&#43;<o:p></o:p></span></p> <p \
class="MsoNormal"><o:p>&nbsp;</o:p></p> <div>
<p class="MsoNormal">Please make such programs crash early and often.&nbsp; They are \
a nightmare to maintain.&nbsp; Make them blow in the face of the original authors; \
not after they are gone.<o:p></o:p></p> <div>
<p class="MsoNormal"><o:p>&nbsp;</o:p></p>
</div>
<div>
<p class="MsoNormal">-- Gaby<o:p></o:p></p>
<div>
<p class="MsoNormal"><o:p>&nbsp;</o:p></p>
</div>
</div>
</div>
</div>
<br>
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the intended recipient, please notify the sender immediately and do not disclose the \
contents  to any other person, use it for any purpose, or store or copy the \
information in any medium. Thank you.<br> <br>
ARM Limited, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, Registered in \
England &amp; Wales, Company No: 2557590<br> ARM Holdings plc, Registered office 110 \
Fulbourn Road, Cambridge CB1 9NJ, Registered in England &amp; Wales, Company No: \
2548782<br> </font>
</body>
</html>


["0001-Always-trap-for-missing-return-statements-except-whe.patch" (application/octet-stream)]

From 0ee50b3f8d7f247af358b75d0e0741308af647e9 Mon Sep 17 00:00:00 2001
From: Sjoerd Meijer <sjoerd.meijer@arm.com>
Date: Mon, 17 Aug 2015 11:38:35 +0100
Subject: [PATCH] Always trap for missing return statements, except when
 optimizing for size.

---
 lib/CodeGen/CodeGenFunction.cpp | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/lib/CodeGen/CodeGenFunction.cpp b/lib/CodeGen/CodeGenFunction.cpp
index 9bf4161..3135c1a 100644
--- a/lib/CodeGen/CodeGenFunction.cpp
+++ b/lib/CodeGen/CodeGenFunction.cpp
@@ -926,7 +926,14 @@ void CodeGenFunction::GenerateCode(GlobalDecl GD, llvm::Function *Fn,
       EmitCheck(std::make_pair(IsFalse, SanitizerKind::Return),
                 "missing_return", EmitCheckSourceLocation(FD->getLocation()),
                 None);
-    } else if (CGM.getCodeGenOpts().OptimizationLevel == 0) {
+    } 
+
+    // A missing return statement provides opportunities for optimizing away
+    // unreachable control flow, i.e it is a code-size optimization opportunity. 
+    // However, not returning from a function is potentially unsafe and also not 
+    // so user-friendly. Therefore, we trap for all optimizations levels, except 
+    // when optimizing for size.
+    if (!CGM.getCodeGenOpts().OptimizeSize) {
       EmitTrapCall(llvm::Intrinsic::trap);
     }
     Builder.CreateUnreachable();
-- 
1.9.1


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