https://llvm.org/bugs/show_bug.cgi?id=25867
Bug ID: 25867
Summary: Inconsistency in dereferencing of void pointers
Product: clang
Version: 3.7
Hardware: All
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Frontend
Assignee: unassignedclangb...@nondot.org
Reporter: baranniko...@gmail.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
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
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