diff options
Diffstat (limited to 'llvm/lib/Transforms/Scalar/IndVarSimplify.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Scalar/IndVarSimplify.cpp | 24 |
1 files changed, 20 insertions, 4 deletions
diff --git a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp index 5d1bb6b9390..246ddfd28f6 100644 --- a/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp +++ b/llvm/lib/Transforms/Scalar/IndVarSimplify.cpp @@ -628,13 +628,29 @@ bool IndVarSimplify::rewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) { // Okay, this instruction has a user outside of the current loop // and varies predictably *inside* the loop. Evaluate the value it - // contains when the loop exits, if possible. + // contains when the loop exits, if possible. We prefer to start with + // expressions which are true for all exits (so as to maximize + // expression reuse by the SCEVExpander), but resort to per-exit + // evaluation if that fails. const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop()); if (isa<SCEVCouldNotCompute>(ExitValue) || !SE->isLoopInvariant(ExitValue, L) || - !isSafeToExpand(ExitValue, *SE)) - continue; - + !isSafeToExpand(ExitValue, *SE)) { + // TODO: This should probably be sunk into SCEV in some way; maybe a + // getSCEVForExit(SCEV*, L, ExitingBB)? It can be generalized for + // most SCEV expressions and other recurrence types (e.g. shift + // recurrences). Is there existing code we can reuse? + const SCEV *ExitCount = SE->getExitCount(L, PN->getIncomingBlock(i)); + if (isa<SCEVCouldNotCompute>(ExitCount)) + continue; + if (auto *AddRec = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Inst))) + ExitValue = AddRec->evaluateAtIteration(ExitCount, *SE); + if (isa<SCEVCouldNotCompute>(ExitValue) || + !SE->isLoopInvariant(ExitValue, L) || + !isSafeToExpand(ExitValue, *SE)) + continue; + } + // Computing the value outside of the loop brings no benefit if it is // definitely used inside the loop in a way which can not be optimized // away. Avoid doing so unless we know we have a value which computes |
