<div dir="ltr"><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Mar 11, 2019 at 3:38 AM Benjamin Kramer via llvm-commits <<a href="mailto:llvm-commits@lists.llvm.org">llvm-commits@lists.llvm.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Author: d0k<br>
Date: Mon Mar 11 03:39:15 2019<br>
New Revision: 355818<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=355818&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project?rev=355818&view=rev</a><br>
Log:<br>
[MIPS GlobalISel] Silence uninitialized variable warning<br>
<br>
The control flow here cannot ever use the uninitialized value, but it's<br>
too hard for the compiler to figure that out. Clang warns:<br></blockquote><div><br>Clang's uninitialized warning is pretty careful about false positives - I beileve you either need an always-true condition (might happen if you do something like "if (sizeof(int) == 4) else if (sizeof(int) == 8)", for instance) or it really is use-of-uninitialized.<br><br>In this case it looks like CarrySum is assigned to CarrySumPrevDstIdx unconditionally after the if/else, but is not initialized in the else block at all. That seems like a true-positive & an open question as to what value should be assigned to CarrySum in the else block, right? Is this codepath tested & is the zero the right answer here?<br> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp:2600:28: error: variable 'CarrySum' is used uninitialized whenever 'for' loop exits because its condition is false [-Werror,-Wsometimes-uninitialized]<br>
      for (unsigned i = 2; i < Factors.size(); ++i)<br>
                           ^~~~~~~~~~~~~~~~~~<br>
llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp:2604:26: note: uninitialized use occurs here<br>
    CarrySumPrevDstIdx = CarrySum;<br>
                         ^~~~~~~~<br>
llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp:2600:28: note: remove the condition if it is always true<br>
      for (unsigned i = 2; i < Factors.size(); ++i)<br>
                           ^~~~~~~~~~~~~~~~~~<br>
llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp:2583:22: note: initialize the variable 'CarrySum' to silence this warning<br>
    unsigned CarrySum;<br>
                     ^<br>
                      = 0<br>
<br>
Modified:<br>
    llvm/trunk/lib/CodeGen/GlobalISel/LegalizerHelper.cpp<br>
<br>
Modified: llvm/trunk/lib/CodeGen/GlobalISel/LegalizerHelper.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/GlobalISel/LegalizerHelper.cpp?rev=355818&r1=355817&r2=355818&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/GlobalISel/LegalizerHelper.cpp?rev=355818&r1=355817&r2=355818&view=diff</a><br>
==============================================================================<br>
--- llvm/trunk/lib/CodeGen/GlobalISel/LegalizerHelper.cpp (original)<br>
+++ llvm/trunk/lib/CodeGen/GlobalISel/LegalizerHelper.cpp Mon Mar 11 03:39:15 2019<br>
@@ -2581,7 +2581,7 @@ void LegalizerHelper::multiplyRegisters(<br>
       Factors.push_back(CarrySumPrevDstIdx);<br>
     }<br>
<br>
-    unsigned CarrySum;<br>
+    unsigned CarrySum = 0;<br>
     // Add all factors and accumulate all carries into CarrySum.<br>
     if (DstIdx != DstParts - 1) {<br>
       MachineInstrBuilder Uaddo =<br>
<br>
<br>
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</blockquote></div></div>