http://llvm.org/bugs/show_bug.cgi?id=15727
Bug ID: 15727
Summary: Value::isUsedInBasicBlock is buggy.
Product: libraries
Version: 3.2
Hardware: PC
OS: Linux
Status: NEW
Severity: release blocker
Priority: P
Component: Core LLVM classes
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
I happened to use Value::isUsedInBasicBlock(const BasicBlock *BB) const.
I noticed that the function always returns false when the basic block size is
larger than 3. So I checked the source of Value.c and found there is a bug
there.
113 unsigned MaxBlockSize = 3;
114 for (BasicBlock::const_iterator I = BB->begin(), E = BB->end(); I != E;
++I) {
115 if (std::find(I->op_begin(), I->op_end(), this) != I->op_end())
116 return true;
117 if (MaxBlockSize-- == 0) // If the block is larger fall back to
use_iterator
118 break;
119 }
120
121 if (MaxBlockSize != 0) // We scanned the entire block and found no use.
122 return false;
If block size is larger than 3, in line 117, the loop is breaked out, and
MaxBlockSize = -1. In line 121, MaxBlockSize != 0 is true, and false is
returned. This explains why the function always returns false when the block
size is larger than 3.
The potential bug fix is
117 if (--MaxBlockSize == 0) // If ...
Thanks!
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