Don't crash on extra evil irreducible control flow.

When the CFG contains a loop with multiple entry blocks, the traces
computed by MachineTraceMetrics don't always have the same nice
properties. Loop back-edges are normally excluded from traces, but
MachineLoopInfo doesn't recognize loops with multiple entry blocks, so
those back-edges may be included.

Avoid asserting when that happens by adding an isEarlierInSameTrace()
function that accurately determines if a dominating block is part of the
same trace AND is above the currrent block in the trace.

llvm-svn: 165434

2 files changed, 10 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/MachineTraceMetrics.cpp b/llvm/lib/CodeGen/MachineTraceMetrics.cpp
index 9b91af541db..b3abec76bc9 100644
--- a/llvm/lib/CodeGen/MachineTraceMetrics.cpp
+++ b/llvm/lib/CodeGen/MachineTraceMetrics.cpp
@@ -677,7 +677,7 @@ computeCrossBlockCriticalPath(const TraceBlockInfo &TBI) {
     const MachineInstr *DefMI = MTM.MRI->getVRegDef(LIR.Reg);
     // Ignore dependencies outside the current trace.
     const TraceBlockInfo &DefTBI = BlockInfo[DefMI->getParent()->getNumber()];
-    if (!DefTBI.hasValidDepth() || DefTBI.Head != TBI.Head)
+    if (!DefTBI.isEarlierInSameTrace(TBI))
       continue;
     unsigned Len = LIR.Height + Cycles[DefMI].Depth;
     MaxLen = std::max(MaxLen, Len);
@@ -740,7 +740,7 @@ computeInstrDepths(const MachineBasicBlock *MBB) {
         const TraceBlockInfo&DepTBI =
           BlockInfo[Dep.DefMI->getParent()->getNumber()];
         // Ignore dependencies from outside the current trace.
-        if (!DepTBI.hasValidDepth() || DepTBI.Head != TBI.Head)
+        if (!DepTBI.isEarlierInSameTrace(TBI))
           continue;
         assert(DepTBI.HasValidInstrDepths && "Inconsistent dependency");
         unsigned DepCycle = Cycles.lookup(Dep.DefMI).Depth;
diff --git a/llvm/lib/CodeGen/MachineTraceMetrics.h b/llvm/lib/CodeGen/MachineTraceMetrics.h
index d329c51634a..5f3b1d23e41 100644
--- a/llvm/lib/CodeGen/MachineTraceMetrics.h
+++ b/llvm/lib/CodeGen/MachineTraceMetrics.h
@@ -165,6 +165,14 @@ public:
     /// Invalidate height resources when a block below this one has changed.
     void invalidateHeight() { InstrHeight = ~0u; HasValidInstrHeights = false; }
 
+    /// Determine if this block belongs to the same trace as TBI and comes
+    /// before it in the trace.
+    /// Also returns true when TBI == this.
+    bool isEarlierInSameTrace(const TraceBlockInfo &TBI) const {
+      return hasValidDepth() && TBI.hasValidDepth() &&
+        Head == TBI.Head && InstrDepth <= TBI.InstrDepth;
+    }
+
     // Data-dependency-related information. Per-instruction depth and height
     // are computed from data dependencies in the current trace, using
     // itinerary data.