Fix PR 24723 - Handle 0-mass backedges in irreducible loops

This corner case happens when we have an irreducible SCC that is
deeply nested.  As we work down the tree, the backedge masses start
getting smaller and smaller until we reach one that is down to 0.

Since we distribute the incoming mass using the backedge masses as
weight, the distributor does not allow zero weights.  So, we simply
ignore them (which will just use the weights of the non-zero nodes).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247050 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/BlockFrequencyInfoImpl.cpp b/lib/Analysis/BlockFrequencyInfoImpl.cpp
index 6ceda06..903a263 100644 (file)
--- a/lib/Analysis/BlockFrequencyInfoImpl.cpp
+++ b/lib/Analysis/BlockFrequencyInfoImpl.cpp
@@ -743,7 +743,10 @@ void BlockFrequencyInfoImplBase::adjustLoopHeaderMass(LoopData &Loop) {
     auto &BackedgeMass = Loop.BackedgeMass[Loop.getHeaderIndex(HeaderNode)];
     DEBUG(dbgs() << " - Add back edge mass for node "
                  << getBlockName(HeaderNode) << ": " << BackedgeMass << "\n");
-    Dist.addLocal(HeaderNode, BackedgeMass.getMass());
+    if (BackedgeMass.getMass() > 0)
+      Dist.addLocal(HeaderNode, BackedgeMass.getMass());
+    else
+      DEBUG(dbgs() << "   Nothing added. Back edge mass is zero\n");
   }
 
   DitheringDistributer D(Dist, LoopMass);

diff --git a/test/Analysis/BlockFrequencyInfo/irreducible_loop_crash.ll b/test/Analysis/BlockFrequencyInfo/irreducible_loop_crash.ll
new file mode 100644 (file)
index 0000000..2bcd088
--- /dev/null
+++ b/test/Analysis/BlockFrequencyInfo/irreducible_loop_crash.ll
@@ -0,0 +1,155 @@
+; RUN: opt < %s -analyze -block-freq
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @fn1(i32* %f) {
+entry:
+  %tobool7 = icmp eq i32 undef, 0
+  br i1 undef, label %if.end.12, label %for.body.5
+
+for.inc:
+  store i32 undef, i32* %f, align 4
+  br label %for.body.5
+
+for.body.5:                                       ; preds = %for.cond.4.preheader
+  br i1 %tobool7, label %for.inc.9, label %for.inc
+
+for.inc.9:                                        ; preds = %for.body.5
+  br i1 %tobool7, label %for.inc.9.1, label %for.inc
+
+if.end.12:                                        ; preds = %if.end.12, %for.body
+  br i1 undef, label %for.end.17, label %for.inc
+
+for.end.17:                                       ; preds = %entry
+  ret void
+
+for.inc.9.1:                                      ; preds = %for.inc.9
+  br i1 %tobool7, label %for.inc.9.2, label %for.inc
+
+for.inc.9.2:                                      ; preds = %for.inc.9.1
+  br i1 %tobool7, label %for.inc.9.3, label %for.inc
+
+for.inc.9.3:                                      ; preds = %for.inc.9.2
+  br i1 %tobool7, label %for.inc.9.4, label %for.inc
+
+for.inc.9.4:                                      ; preds = %for.inc.9.3
+  br i1 %tobool7, label %for.inc.9.5, label %for.inc
+
+for.inc.9.5:                                      ; preds = %for.inc.9.4
+  br i1 %tobool7, label %for.inc.9.6, label %for.inc
+
+for.inc.9.6:                                      ; preds = %for.inc.9.5
+  br i1 %tobool7, label %for.inc.9.7, label %for.inc
+
+for.inc.9.7:                                      ; preds = %for.inc.9.6
+  br i1 %tobool7, label %for.inc.9.8, label %for.inc
+
+for.inc.9.8:                                      ; preds = %for.inc.9.7
+  br i1 %tobool7, label %for.inc.9.9, label %for.inc
+
+for.inc.9.9:                                      ; preds = %for.inc.9.8
+  br i1 %tobool7, label %for.inc.9.10, label %for.inc
+
+for.inc.9.10:                                     ; preds = %for.inc.9.9
+  br i1 %tobool7, label %for.inc.9.11, label %for.inc
+
+for.inc.9.11:                                     ; preds = %for.inc.9.10
+  br i1 %tobool7, label %for.inc.9.12, label %for.inc
+
+for.inc.9.12:                                     ; preds = %for.inc.9.11
+  br i1 %tobool7, label %for.inc.9.13, label %for.inc
+
+for.inc.9.13:                                     ; preds = %for.inc.9.12
+  br i1 %tobool7, label %for.inc.9.14, label %for.inc
+
+for.inc.9.14:                                     ; preds = %for.inc.9.13
+  br i1 %tobool7, label %for.inc.9.15, label %for.inc
+
+for.inc.9.15:                                     ; preds = %for.inc.9.14
+  br i1 %tobool7, label %for.inc.9.16, label %for.inc
+
+for.inc.9.16:                                     ; preds = %for.inc.9.15
+  br i1 %tobool7, label %for.inc.9.17, label %for.inc
+
+for.inc.9.17:                                     ; preds = %for.inc.9.16
+  br i1 %tobool7, label %for.inc.9.18, label %for.inc
+
+for.inc.9.18:                                     ; preds = %for.inc.9.17
+  br i1 %tobool7, label %for.inc.9.19, label %for.inc
+
+for.inc.9.19:                                     ; preds = %for.inc.9.18
+  br i1 %tobool7, label %for.inc.9.20, label %for.inc
+
+for.inc.9.20:                                     ; preds = %for.inc.9.19
+  br i1 %tobool7, label %for.inc.9.21, label %for.inc
+
+for.inc.9.21:                                     ; preds = %for.inc.9.20
+  br i1 %tobool7, label %for.inc.9.22, label %for.inc
+
+for.inc.9.22:                                     ; preds = %for.inc.9.21
+  br i1 %tobool7, label %for.inc.9.23, label %for.inc
+
+for.inc.9.23:                                     ; preds = %for.inc.9.22
+  br i1 %tobool7, label %for.inc.9.24, label %for.inc
+
+for.inc.9.24:                                     ; preds = %for.inc.9.23
+  br i1 %tobool7, label %for.inc.9.25, label %for.inc
+
+for.inc.9.25:                                     ; preds = %for.inc.9.24
+  br i1 %tobool7, label %for.inc.9.26, label %for.inc
+
+for.inc.9.26:                                     ; preds = %for.inc.9.25
+  br i1 %tobool7, label %for.inc.9.27, label %for.inc
+
+for.inc.9.27:                                     ; preds = %for.inc.9.26
+  br i1 %tobool7, label %for.inc.9.28, label %for.inc
+
+for.inc.9.28:                                     ; preds = %for.inc.9.27
+  br i1 %tobool7, label %for.inc.9.29, label %for.inc
+
+for.inc.9.29:                                     ; preds = %for.inc.9.28
+  br i1 %tobool7, label %for.inc.9.30, label %for.inc
+
+for.inc.9.30:                                     ; preds = %for.inc.9.29
+  br i1 %tobool7, label %for.inc.9.31, label %for.inc
+
+for.inc.9.31:                                     ; preds = %for.inc.9.30
+  br i1 %tobool7, label %for.inc.9.32, label %for.inc
+
+for.inc.9.32:                                     ; preds = %for.inc.9.31
+  br i1 %tobool7, label %for.inc.9.33, label %for.inc
+
+for.inc.9.33:                                     ; preds = %for.inc.9.32
+  br i1 %tobool7, label %for.inc.9.34, label %for.inc
+
+for.inc.9.34:                                     ; preds = %for.inc.9.33
+  br i1 %tobool7, label %for.inc.9.35, label %for.inc
+
+for.inc.9.35:                                     ; preds = %for.inc.9.34
+  br i1 %tobool7, label %for.inc.9.36, label %for.inc
+
+for.inc.9.36:                                     ; preds = %for.inc.9.35
+  br i1 %tobool7, label %for.inc.9.37, label %for.inc
+
+for.inc.9.37:                                     ; preds = %for.inc.9.36
+  br i1 %tobool7, label %for.inc.9.38, label %for.inc
+
+for.inc.9.38:                                     ; preds = %for.inc.9.37
+  br i1 %tobool7, label %for.inc.9.39, label %for.inc
+
+for.inc.9.39:                                     ; preds = %for.inc.9.38
+  br i1 %tobool7, label %for.inc.9.40, label %for.inc
+
+for.inc.9.40:                                     ; preds = %for.inc.9.39
+  br i1 %tobool7, label %for.inc.9.41, label %for.inc
+
+for.inc.9.41:                                     ; preds = %for.inc.9.40
+  br i1 %tobool7, label %for.inc.9.42, label %for.inc
+
+for.inc.9.42:                                     ; preds = %for.inc.9.41
+  br i1 %tobool7, label %for.inc.9.43, label %for.inc
+
+for.inc.9.43:                                     ; preds = %for.inc.9.42
+  br i1 %tobool7, label %if.end.12, label %for.inc
+}