BFI: Saturate when combining edges to a successor
When a loop gets bundled up, its outgoing edges are quite large, and can
just barely overflow 64-bits. If one successor has multiple incoming
edges -- and that successor is getting all the incoming mass --
combining just its edges can overflow. Handle that by saturating rather
than asserting.
This fixes PR21622.
llvm-svn: 223500
diff --git a/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp b/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
index 06b8acd..278073c 100644
--- a/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
+++ b/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
@@ -14,6 +14,7 @@
#include "llvm/Analysis/BlockFrequencyInfoImpl.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/Support/raw_ostream.h"
+#include <numeric>
using namespace llvm;
using namespace llvm::bfi_detail;
@@ -122,8 +123,12 @@
}
assert(W.Type == OtherW.Type);
assert(W.TargetNode == OtherW.TargetNode);
- assert(W.Amount < W.Amount + OtherW.Amount && "Unexpected overflow");
- W.Amount += OtherW.Amount;
+ assert(OtherW.Amount && "Expected non-zero weight");
+ if (W.Amount > W.Amount + OtherW.Amount)
+ // Saturate on overflow.
+ W.Amount = UINT64_MAX;
+ else
+ W.Amount += OtherW.Amount;
}
static void combineWeightsBySorting(WeightList &Weights) {
// Sort so edges to the same node are adjacent.
@@ -206,11 +211,19 @@
Shift = 33 - countLeadingZeros(Total);
// Early exit if nothing needs to be scaled.
- if (!Shift)
+ if (!Shift) {
+ // If we didn't overflow then combineWeights() shouldn't have changed the
+ // sum of the weights, but let's double-check.
+ assert(Total == std::accumulate(Weights.begin(), Weights.end(), UINT64_C(0),
+ [](uint64_t Sum, const Weight &W) {
+ return Sum + W.Amount;
+ }) &&
+ "Expected total to be correct");
return;
+ }
// Recompute the total through accumulation (rather than shifting it) so that
- // it's accurate after shifting.
+ // it's accurate after shifting and any changes combineWeights() made above.
Total = 0;
// Sum the weights to each node and shift right if necessary.