Remove an incorrect assert during branch weight propagation.

Patch and test case by Alastair Murray!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163437 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Utils/SimplifyCFG.cpp

@@ -929,7 +929,6 @@ bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
                                 GetWeight(TI, i)->getValue().getZExtValue());
             } else if (PredHasWeights) {
               // Split the old default's weight amongst the children
-              assert(PredDefaultWeight != 0);
               Weights.push_back(PredDefaultWeight / (1 + BBCases.size()));
             }
           }

test/Transforms/SimplifyCFG/preserve-branchweights-partial.ll

@@ -0,0 +1,37 @@
+; RUN: opt -simplifycfg -S -o - < %s | FileCheck %s
+
+; This test case was written to trigger an incorrect assert statement in
+; -simplifycfg.  Thus we don't actually want to check the output, just that
+; -simplifycfg ran successfully.  Thus we only check that the function still
+; exists, and that it still calls foo().
+;
+; NOTE: There are some obviously dead blocks and missing branch weight
+;       metadata.  Both of these features were key to triggering the assert.
+;       Additionally, the not-taken weight of the branch with a weight had to
+;       be 0 to trigger the assert.
+
+declare void @foo() nounwind uwtable
+
+define void @func(i32 %A) nounwind uwtable {
+; CHECK: define void @func
+entry:
+  %cmp11 = icmp eq i32 %A, 1
+  br i1 %cmp11, label %if.then, label %if.else, !prof !0
+
+if.then:
+  call void @foo()
+; CHECK: call void @foo()
+  br label %if.else
+
+if.else:
+  %cmp17 = icmp eq i32 %A, 2
+  br i1 %cmp17, label %if.then2, label %if.end
+
+if.then2:
+  br label %if.end
+
+if.end:
+  ret void
+}
+
+!0 = metadata !{metadata !"branch_weights", i32 1, i32 0}