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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Inconsistency in dereferencing of void pointers"
href="https://llvm.org/bugs/show_bug.cgi?id=25867">25867</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Inconsistency in dereferencing of void pointers
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.7
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Frontend
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>barannikov88@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Consider the following example:
void f()
{
void *p1;
volatile void *p2;
*p1;
*p2;
p1[0];
p2[0];
}
All of operations on p1 and p2 are dereferencing operations ((C99 6.5.2.1p2 The
definition of the subscript operator [] is that E1[E2] is identical to
(*((E1)+(E2))).), but they are treated differently when generating llvm IR:
// %p1 = alloca i8*, align 4
// %p2 = alloca i8*, align 4
*p1;
// %0 = load i8*, i8** %p1, align 4
*p2;
// %1 = load i8*, i8** %p2, align 4
p1[0];
// %2 = load i8*, i8** %p1, align 4
// %arrayidx = getelementptr inbounds i8, i8* %2, i32 0
// %3 = load i8, i8* %arrayidx
p2[0];
// %4 = load i8*, i8** %p2, align 4
// %arrayidx1 = getelementptr inbounds i8, i8* %4, i32 0
// ret void
Operation p1[0] does load, others do not.
Also, '*p2' and 'p2[0]' are lvalues, while '*p1' and 'p1[0]' are not:
|-UnaryOperator 0xf688c88 <line:6:5, col:6> 'void' prefix '*'
| `-ImplicitCastExpr 0xf688c78 <col:6> 'void *' <LValueToRValue>
| `-DeclRefExpr 0xf688c60 <col:6> 'void *' lvalue Var 0xf688ba0 'p1'
'void *'
|-UnaryOperator 0xf688cc8 <line:9:5, col:6> 'volatile void' lvalue prefix
'*'
| `-ImplicitCastExpr 0xf688cb8 <col:6> 'volatile void *' <LValueToRValue>
| `-DeclRefExpr 0xf688c9c <col:6> 'volatile void *' lvalue Var 0xf688c18
'p2' 'volatile void *'
|-ArraySubscriptExpr 0xf688d20 <line:12:5, col:9> 'void'
| |-ImplicitCastExpr 0xf688d10 <col:5> 'void *' <LValueToRValue>
| | `-DeclRefExpr 0xf688cdc <col:5> 'void *' lvalue Var 0xf688ba0 'p1'
'void *'
| `-IntegerLiteral 0xf688cf8 <col:8> 'int' 0
`-ArraySubscriptExpr 0xf688d78 <line:17:5, col:9> 'volatile void' lvalue
|-ImplicitCastExpr 0xf688d68 <col:5> 'volatile void *' <LValueToRValue>
| `-DeclRefExpr 0xf688d34 <col:5> 'volatile void *' lvalue Var 0xf688c18
'p2' 'volatile void *'
`-IntegerLiteral 0xf688d50 <col:8> 'int' 0</pre>
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