https://llvm.org/bugs/show_bug.cgi?id=27360
Bug ID: 27360
Summary: LLVM cannot unroll loops with multiple exits
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Keywords: googler, performance
Severity: normal
Priority: P
Component: Loop Optimizer
Assignee: unassignedb...@nondot.org
Reporter: daniel...@gmail.com
CC: davi...@google.com, llvm-bugs@lists.llvm.org
Classification: Unclassified
For the following test case:
bool foo(int i, int *m) {
int w = m[i];
#pragma unroll 8
while (w == 0) {
if (--i < 0) return false;
w = m[i];
}
return true;
}
"g++ -O2 -funroll-all-loops" can successfully unroll this loop (even without
pragma).
But LLVM rejects unrolling this loop because:
284│ // For now, only unroll loops that contain a single exit.
285├> if (!L->getExitingBlock())
286│ return false;
This makes llvm missing many optimization opportunities.
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