From 7f7263354767fb201c53da88b83d1ec4e3511432 Mon Sep 17 00:00:00 2001 From: Andrew Trick Date: Mon, 7 Apr 2014 21:29:22 +0000 Subject: [PATCH] Put a limit on ScheduleDAGSDNodes::ClusterNeighboringLoads to avoid blowing up compile time. Fixes PR16365 - Extremely slow compilation in -O1 and -O2. The SD scheduler has a quadratic implementation of load clustering which absolutely blows up compile time for large blocks with constant pool loads. The MI scheduler has a better implementation of load clustering. However, we have not done the work yet to completely eliminate the SD scheduler. Some benchmarks still seem to benefit from early load clustering, although maybe by chance. As an intermediate term fix, I just put a nice limit on the number of DAG users to search before finding a match. With this limit there are no binary differences in the LLVM test suite, and the PR16365 test case does not suffer any compile time impact from this routine. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205738 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp index 5639894d096f3..ae9a580184d1e 100644 --- a/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp +++ b/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp @@ -219,8 +219,11 @@ void ScheduleDAGSDNodes::ClusterNeighboringLoads(SDNode *Node) { DenseMap O2SMap; // Map from offset to SDNode. bool Cluster = false; SDNode *Base = Node; + // This algorithm requires a reasonably low use count before finding a match + // to avoid uselessly blowing up compile time in large blocks. + unsigned UseCount = 0; for (SDNode::use_iterator I = Chain->use_begin(), E = Chain->use_end(); - I != E; ++I) { + I != E && UseCount < 100; ++I, ++UseCount) { SDNode *User = *I; if (User == Node || !Visited.insert(User)) continue; @@ -237,6 +240,8 @@ void ScheduleDAGSDNodes::ClusterNeighboringLoads(SDNode *Node) { if (Offset2 < Offset1) Base = User; Cluster = true; + // Reset UseCount to allow more matches. + UseCount = 0; } if (!Cluster)