[PATCH] D120752: [RegAlloc] Add a complexity limit in growRegion() to cap compilation time.
Vasileios Porpodas via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Mar 1 10:25:56 PST 2022
vporpo created this revision.
vporpo added reviewers: qcolombet, wenlei.
Herald added subscribers: hiraditya, MatzeB.
vporpo requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.
growRegion() does not scale in code with BBs with a very large number of edges.
In such code growRegion() becomes a compile-time bottleneck, consuming 60% of
the total compilation time.
This patch adds a limit to the time spent in growRegion(). We bail out once
the limit is reached.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D120752
Files:
llvm/lib/CodeGen/RegAllocGreedy.cpp
Index: llvm/lib/CodeGen/RegAllocGreedy.cpp
===================================================================
--- llvm/lib/CodeGen/RegAllocGreedy.cpp
+++ llvm/lib/CodeGen/RegAllocGreedy.cpp
@@ -133,6 +133,12 @@
"candidate when choosing the best split candidate."),
cl::init(false));
+static cl::opt<long> GrowRegionComplexityBudget(
+ "grow-region-complexity-budget",
+ cl::desc("growRegion() does not scale, so limit its budget. "
+ "Bail out if we explore this many edges."),
+ cl::init(10000), cl::Hidden);
+
static RegisterRegAlloc greedyRegAlloc("greedy", "greedy register allocator",
createGreedyRegisterAllocator);
@@ -784,6 +790,7 @@
unsigned Visited = 0;
#endif
+ long Budget = GrowRegionComplexityBudget;
while (true) {
ArrayRef<unsigned> NewBundles = SpillPlacer->getRecentPositive();
// Find new through blocks in the periphery of PrefRegBundles.
@@ -791,6 +798,9 @@
// Look at all blocks connected to Bundle in the full graph.
ArrayRef<unsigned> Blocks = Bundles->getBlocks(Bundle);
for (unsigned Block : Blocks) {
+ // Limit compilation time by bailing out after we use all our budget.
+ if (Budget-- == 0)
+ return false;
if (!Todo.test(Block))
continue;
Todo.reset(Block);
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