[llvm-commits] [llvm] r98023 - /llvm/trunk/lib/CodeGen/SimpleRegisterCoalescing.cpp

[Jakob Stoklund Olesen]

Author: stoklund
Date: Mon Mar  8 18:59:48 2010
New Revision: 98023

URL: http://llvm.org/viewvc/llvm-project?rev=98023&view=rev
Log:
Disable physical register coalescing when the number of live ranges for the
physreg becomes ridiculously high.

std::upper_bound may be log(N), but for sufficiently large live intervals, it
becomes log(N)*cachemiss = a long long time.

This patch improves coalescer time by 4500x for a function with 20000
function calls. The generated code is different, but not significantly worse -
the allocator hints are almost as good as physreg coalescing anyway.

Modified:
    llvm/trunk/lib/CodeGen/SimpleRegisterCoalescing.cpp

Modified: llvm/trunk/lib/CodeGen/SimpleRegisterCoalescing.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SimpleRegisterCoalescing.cpp?rev=98023&r1=98022&r2=98023&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SimpleRegisterCoalescing.cpp (original)
+++ llvm/trunk/lib/CodeGen/SimpleRegisterCoalescing.cpp Mon Mar  8 18:59:48 2010
@@ -1671,8 +1671,20 @@
         // density, do not join them, instead mark the physical register as its
         // allocation preference.
         LiveInterval &JoinVInt = SrcIsPhys ? DstInt : SrcInt;
+        LiveInterval &JoinPInt = SrcIsPhys ? SrcInt : DstInt;
         unsigned JoinVReg = SrcIsPhys ? DstReg : SrcReg;
         unsigned JoinPReg = SrcIsPhys ? SrcReg : DstReg;
+
+        // Don't join with physregs that have a ridiculous number of live
+        // ranges. The data structure performance is really bad when that
+        // happens.
+        if (JoinPInt.ranges.size() > 1000) {
+          mri_->setRegAllocationHint(JoinVInt.reg, 0, JoinPReg);
+          ++numAborts;
+          DEBUG(dbgs() << "\tPhysical register too complicated, abort!\n");
+          return false;
+        }
+
         const TargetRegisterClass *RC = mri_->getRegClass(JoinVReg);
         unsigned Threshold = allocatableRCRegs_[RC].count() * 2;
         unsigned Length = li_->getApproximateInstructionCount(JoinVInt);