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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [DebugInfo][Dexter] Speculated BB presents illegal variable value to debugger"
href="https://bugs.llvm.org/show_bug.cgi?id=38763">38763</a>
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<th>Summary</th>
<td>[DebugInfo][Dexter] Speculated BB presents illegal variable value to debugger
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<th>Product</th>
<td>new-bugs
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<th>Version</th>
<td>trunk
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>new bugs
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>jeremy.morse.llvm@gmail.com
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<th>CC</th>
<td>chackz0x12@gmail.com, greg.bedwell@sony.com, international.phantom@gmail.com, llvm-bugs@lists.llvm.org, paul_robinson@playstation.sony.com
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<p>
<div>
<pre>Speculating a basic block into a select IR insn causes an illegal variable
value to be presented to the debugger. Taking the code below, compiled -O2 -g
for x86_64 with trunk, on the line "if (read == 4)" both gdb and lldb report
that the value of "result" is two, where it should be zero.
The value two isn't calculated in the execution of this program, and when
compiled with -O0 "result" is correctly reported zero on that line. More
interestingly, the illegal value doesn't actually seem to be read from a
speculated instruction, "result" is reported as two from the moment the
volatile loads are done.
I get the impression that something DWARFy is going wrong, as the
DW_AT_location expression for "result" looks way more complicated that it needs
to be.
Found using DExTer ( <a href="https://github.com/SNSystems/dexter">https://github.com/SNSystems/dexter</a> ).
-------->8--------
int
main()
{
volatile int foo = 4;
int read = foo;
int read1 = foo;
int result = 0;
if (read == 4) {
result = read1 + 2;
} else {
result = read1 - 2;
}
return result;
}
--------8<--------</pre>
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