https://bugs.llvm.org/show_bug.cgi?id=47308
Bug ID: 47308
Summary: Loop vectorizer causes crash when compiler -
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Loop Optimizer
Assignee: unassignedb...@nondot.org
Reporter: praha...@ualberta.ca
CC: llvm-bugs@lists.llvm.org
compile command:
./clang -Os -mllvm -force-vector-width=4 bug_test.c -S -emit-llvm -o bug_os.ll
source:
bug_test.c
include <stdio.h>
int a;
int main(void) {
int d = -1;
#pragma clang loop vectorize(assume_safety)
for (int i = 0; i < 49; ++i) {
a |= d;
d = i;
}
return 0;
}
The issue is in LoopVectorize.cpp in
LoopVectorizationPlanner::collectTriviallyDeadInstructions. The induction phi
for variable 'c' is marked as dead code here as it is the only use of induction
phi 'd'. Maybe a fix would add a check to ensure the use is not a phi of a
different induction variable. The phi statement being marked as dead code means
it does not get a vectorization recipe and the vector loop body ends up
referring to the original scalar induction variable %c in the vector loop body.
But %c is not defined yet. This causes the assertion in
InnerLoopVectorizer::fixupIVUsers to fail: "Expected LCSSA form".
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