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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165434 91177308-0d34-0410-b5e6-96231b3b80d8

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;

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.

test/CodeGen/X86/early-ifcvt.ll

@@ -67,3 +67,78 @@ if.end41:
 }
 
 declare void @fprintf(...) nounwind
+
+; CHECK: BZ2_decompress
+; This test case contains irreducible control flow, so MachineLoopInfo doesn't
+; recognize the cycle in the CFG. This would confuse MachineTraceMetrics.
+define void @BZ2_decompress(i8* %s) nounwind ssp {
+entry:
+  switch i32 undef, label %sw.default [
+    i32 39, label %if.end.sw.bb2050_crit_edge
+    i32 36, label %sw.bb1788
+    i32 37, label %if.end.sw.bb1855_crit_edge
+    i32 40, label %sw.bb2409
+    i32 38, label %sw.bb1983
+    i32 44, label %if.end.sw.bb3058_crit_edge
+  ]
+
+if.end.sw.bb3058_crit_edge:                       ; preds = %entry
+  br label %save_state_and_return
+
+if.end.sw.bb1855_crit_edge:                       ; preds = %entry
+  br label %save_state_and_return
+
+if.end.sw.bb2050_crit_edge:                       ; preds = %entry
+  br label %sw.bb2050
+
+sw.bb1788:                                        ; preds = %entry
+  br label %save_state_and_return
+
+sw.bb1983:                                        ; preds = %entry
+  br i1 undef, label %save_state_and_return, label %if.then1990
+
+if.then1990:                                      ; preds = %sw.bb1983
+  br label %while.body2038
+
+while.body2038:                                   ; preds = %sw.bb2050, %if.then1990
+  %groupPos.8 = phi i32 [ 0, %if.then1990 ], [ %groupPos.9, %sw.bb2050 ]
+  br i1 undef, label %save_state_and_return, label %if.end2042
+
+if.end2042:                                       ; preds = %while.body2038
+  br i1 undef, label %if.end2048, label %while.end2104
+
+if.end2048:                                       ; preds = %if.end2042
+  %bsLive2054.pre = getelementptr inbounds i8* %s, i32 8
+  br label %sw.bb2050
+
+sw.bb2050:                                        ; preds = %if.end2048, %if.end.sw.bb2050_crit_edge
+  %groupPos.9 = phi i32 [ 0, %if.end.sw.bb2050_crit_edge ], [ %groupPos.8, %if.end2048 ]
+  %and2064 = and i32 undef, 1
+  br label %while.body2038
+
+while.end2104:                                    ; preds = %if.end2042
+  br i1 undef, label %save_state_and_return, label %if.end2117
+
+if.end2117:                                       ; preds = %while.end2104
+  br i1 undef, label %while.body2161.lr.ph, label %while.body2145.lr.ph
+
+while.body2145.lr.ph:                             ; preds = %if.end2117
+  br label %save_state_and_return
+
+while.body2161.lr.ph:                             ; preds = %if.end2117
+  br label %save_state_and_return
+
+sw.bb2409:                                        ; preds = %entry
+  br label %save_state_and_return
+
+sw.default:                                       ; preds = %entry
+  call void @BZ2_bz__AssertH__fail() nounwind
+  br label %save_state_and_return
+
+save_state_and_return:
+  %groupPos.14 = phi i32 [ 0, %sw.default ], [ %groupPos.8, %while.body2038 ], [ %groupPos.8, %while.end2104 ], [ 0, %if.end.sw.bb3058_crit_edge ], [ 0, %if.end.sw.bb1855_crit_edge ], [ %groupPos.8, %while.body2161.lr.ph ], [ %groupPos.8, %while.body2145.lr.ph ], [ 0, %sw.bb2409 ], [ 0, %sw.bb1788 ], [ 0, %sw.bb1983 ]
+  store i32 %groupPos.14, i32* undef, align 4
+  ret void
+}
+
+declare void @BZ2_bz__AssertH__fail()