Compile time decreasing in the case we're dealing with Machine Combiner.

Before this patch compile time was about 21s (see below). After this patch
we have less than 2s (see bellow).

  Intel(R) Xeon(R) CPU E5-2676 v3 @ 2.40GHz

    DAGCombiner - trunk
        time ./llc spill_fdiv.ll -o /dev/null -enable-unsafe-fp-math
        real  0m1.685s

    DAGCombiner + Speed patch
        time ./llc spill_fdiv.ll -o /dev/null -enable-unsafe-fp-math
        real  0m1.655s

    MachineCombiner w/o Speed patch
        time ./llc spill_fdiv.ll -o /dev/null -enable-unsafe-fp-math
        real  0m21.614s

    MachineCombiner + Speed patch
        time ./llc spill_fdiv.ll -o /dev/null -enable-unsafe-fp-math
        real  0m1.593s

The test spill_fdiv.ll  is attached to D29627
D29627 should be closed.

llvm-svn: 294936

1 files changed, 27 insertions, 15 deletions

diff --git a/llvm/lib/CodeGen/MachineCombiner.cpp b/llvm/lib/CodeGen/MachineCombiner.cpp
index 1ec03c0..4a094a1 100644
--- a/llvm/lib/CodeGen/MachineCombiner.cpp
+++ b/llvm/lib/CodeGen/MachineCombiner.cpp
@@ -354,6 +354,19 @@ bool MachineCombiner::doSubstitute(unsigned NewSize, unsigned OldSize) {
   return false;
 }
 
+static void insertDeleteInstructions(MachineBasicBlock *MBB, MachineInstr &MI,
+                                     SmallVector<MachineInstr *, 16> InsInstrs,
+                                     SmallVector<MachineInstr *, 16> DelInstrs,
+                                     MachineTraceMetrics *Traces) {
+  for (auto *InstrPtr : InsInstrs)
+    MBB->insert((MachineBasicBlock::iterator)&MI, InstrPtr);
+  for (auto *InstrPtr : DelInstrs)
+    InstrPtr->eraseFromParentAndMarkDBGValuesForRemoval();
+  ++NumInstCombined;
+  Traces->invalidate(MBB);
+  Traces->verifyAnalysis();
+}
+
 /// Substitute a slow code sequence with a faster one by
 /// evaluating instruction combining pattern.
 /// The prototype of such a pattern is MUl + ADD -> MADD. Performs instruction
@@ -408,7 +421,6 @@ bool MachineCombiner::combineInstructions(MachineBasicBlock *MBB) {
       DenseMap<unsigned, unsigned> InstrIdxForVirtReg;
       if (!MinInstr)
         MinInstr = Traces->getEnsemble(MachineTraceMetrics::TS_MinInstrCount);
-      MachineTraceMetrics::Trace BlockTrace = MinInstr->getTrace(MBB);
       Traces->verifyAnalysis();
       TII->genAlternativeCodeSequence(MI, P, InsInstrs, DelInstrs,
                                       InstrIdxForVirtReg);
@@ -428,23 +440,23 @@ bool MachineCombiner::combineInstructions(MachineBasicBlock *MBB) {
       // fewer instructions OR
       // the new sequence neither lengthens the critical path nor increases
       // resource pressure.
-      if (SubstituteAlways || doSubstitute(NewInstCount, OldInstCount) ||
-          (improvesCriticalPathLen(MBB, &MI, BlockTrace, InsInstrs,
-                                   DelInstrs, InstrIdxForVirtReg, P) &&
-           preservesResourceLen(MBB, BlockTrace, InsInstrs, DelInstrs))) {
-        for (auto *InstrPtr : InsInstrs)
-          MBB->insert((MachineBasicBlock::iterator) &MI, InstrPtr);
-        for (auto *InstrPtr : DelInstrs)
-          InstrPtr->eraseFromParentAndMarkDBGValuesForRemoval();
-
-        Changed = true;
-        ++NumInstCombined;
-
-        Traces->invalidate(MBB);
-        Traces->verifyAnalysis();
+      if (SubstituteAlways || doSubstitute(NewInstCount, OldInstCount)) {
+        insertDeleteInstructions(MBB, MI, InsInstrs, DelInstrs, Traces);
         // Eagerly stop after the first pattern fires.
+        Changed = true;
         break;
       } else {
+        // Calculating the trace metrics may be expensive,
+        // so only do this when necessary.
+        MachineTraceMetrics::Trace BlockTrace = MinInstr->getTrace(MBB);
+        if (improvesCriticalPathLen(MBB, &MI, BlockTrace, InsInstrs, DelInstrs,
+                                    InstrIdxForVirtReg, P) &&
+            preservesResourceLen(MBB, BlockTrace, InsInstrs, DelInstrs)) {
+          insertDeleteInstructions(MBB, MI, InsInstrs, DelInstrs, Traces);
+          // Eagerly stop after the first pattern fires.
+          Changed = true;
+          break;
+        }
         // Cleanup instructions of the alternative code sequence. There is no
         // use for them.
         MachineFunction *MF = MBB->getParent();