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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Instcombine crashes in foldUDivShl when 2nd argument is constant"
href="https://llvm.org/bugs/show_bug.cgi?id=27888">27888</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Instcombine crashes in foldUDivShl when 2nd argument is constant
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>mikael.holmen@ericsson.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>Created <span class=""><a href="attachment.cgi?id=16420" name="attach_16420" title="Reproducer ll file">attachment 16420</a> <a href="attachment.cgi?id=16420&action=edit" title="Reproducer ll file">[details]</a></span>
Reproducer ll file
build-all/bin/opt -S -instcombine -o - ./RM10519_foldUDivShl.ll
gives
opt: ../include/llvm/Support/Casting.h:237: typename cast_retty<X, Y
*>::ret_type llvm::cast(Y *) [X = llvm::Instruction, Y = llvm::Value]:
Assertion `isa<X>(Val) && "cast<Ty>() argument of incompatible type!"' failed.
With -debug:
INSTCOMBINE ITERATION #1 on f1
IC: ADDING: 4 instrs to worklist
IC: Visiting: %_tmp1 = load i16, i16* @g
IC: Visiting: %_tmp2 = udiv i16 %_tmp1, shl (i16 1, i16 zext (i2 ptrtoint
(void ()* @f1 to i2) to i16))
The code crashing is:
// X udiv (C1 << N), where C1 is "1<<C2" --> X >> (N+C2)
static Instruction *foldUDivShl(Value *Op0, Value *Op1, const BinaryOperator
&I,
InstCombiner &IC) {
Instruction *ShiftLeft = cast<Instruction>(Op1);
if (isa<ZExtInst>(ShiftLeft))
ShiftLeft = cast<Instruction>(ShiftLeft->getOperand(0));
const APInt &CI =
cast<Constant>(ShiftLeft->getOperand(0))->getUniqueInteger();
Op1 isn't an Instruction so the cast<Instruction>(Op1) fails.
As seen in the debug printout Op1 is
shl (i16 1, i16 zext (i2 ptrtoint (void ()* @f1 to i2) to i16))
The following change seems to solve the problem:
- Instruction *ShiftLeft = cast<Instruction>(Op1);
- if (isa<ZExtInst>(ShiftLeft))
- ShiftLeft = cast<Instruction>(ShiftLeft->getOperand(0));
+ User *ShiftLeft;
+ if (isa<Constant>(Op1)) {
+ ShiftLeft = cast<User>(Op1);
+ } else {
+ Instruction *ShiftLeftInstr = cast<Instruction>(Op1);
+ if (isa<ZExtInst>(ShiftLeftInstr))
+ ShiftLeftInstr = cast<Instruction>(ShiftLeftInstr->getOperand(0));
+ ShiftLeft = ShiftLeftInstr;
+ }</pre>
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