Prevent binary-tree deterioration in sparse switch statements.
This addresses part of llvm.org/PR22262. Specifically, it prevents
considering the densities of sub-ranges that have fewer than
TLI.getMinimumJumpTableEntries() elements. Those densities won't help
jump tables.
This is not a complete solution but works around the most pressing
issue.
Review: http://reviews.llvm.org/D7070
llvm-svn: 226600
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 2ee276f..ea76bc6 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2420,6 +2420,7 @@
DEBUG(dbgs() << "Selecting best pivot: \n"
<< "First: " << First << ", Last: " << Last <<'\n'
<< "LSize: " << LSize << ", RSize: " << RSize << '\n');
+ const TargetLowering &TLI = DAG.getTargetLoweringInfo();
for (CaseItr I = CR.Range.first, J=I+1, E = CR.Range.second;
J!=E; ++I, ++J) {
const APInt &LEnd = cast<ConstantInt>(I->High)->getValue();
@@ -2429,10 +2430,16 @@
"Invalid case distance");
// Use volatile double here to avoid excess precision issues on some hosts,
// e.g. that use 80-bit X87 registers.
+ // Only consider the density of sub-ranges that actually have sufficient
+ // entries to be lowered as a jump table.
volatile double LDensity =
- LSize.roundToDouble() / (LEnd - First + 1ULL).roundToDouble();
+ LSize.ult(TLI.getMinimumJumpTableEntries())
+ ? 0.0
+ : LSize.roundToDouble() / (LEnd - First + 1ULL).roundToDouble();
volatile double RDensity =
- RSize.roundToDouble() / (Last - RBegin + 1ULL).roundToDouble();
+ RSize.ult(TLI.getMinimumJumpTableEntries())
+ ? 0.0
+ : RSize.roundToDouble() / (Last - RBegin + 1ULL).roundToDouble();
volatile double Metric = Range.logBase2() * (LDensity + RDensity);
// Should always split in some non-trivial place
DEBUG(dbgs() <<"=>Step\n"
@@ -2450,13 +2457,8 @@
RSize -= J->size();
}
- const TargetLowering &TLI = DAG.getTargetLoweringInfo();
- if (areJTsAllowed(TLI)) {
- // If our case is dense we *really* should handle it earlier!
- assert((FMetric > 0) && "Should handle dense range earlier!");
- } else {
+ if (FMetric == 0 || !areJTsAllowed(TLI))
Pivot = CR.Range.first + Size/2;
- }
splitSwitchCase(CR, Pivot, WorkList, SV, SwitchBB);
return true;
}