StackColoring: better handling of statically unreachable code

Summary:
Avoid assert/crash during liveness calculation in situations
where the incoming machine function has statically unreachable BBs.
Second attempt at submitting; this version of the change includes
a revised testcase.

Fixes PR37130.

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D47372

llvm-svn: 333416

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/StackColoring.cpp b/llvm/lib/CodeGen/StackColoring.cpp
index 4f3d1f704aa..0bd941e64aa 100644
--- a/llvm/lib/CodeGen/StackColoring.cpp
+++ b/llvm/lib/CodeGen/StackColoring.cpp
@@ -782,8 +782,11 @@ void StackColoring::calculateLocalLiveness() {
       for (MachineBasicBlock::const_pred_iterator PI = BB->pred_begin(),
            PE = BB->pred_end(); PI != PE; ++PI) {
         LivenessMap::const_iterator I = BlockLiveness.find(*PI);
-        assert(I != BlockLiveness.end() && "Predecessor not found");
-        LocalLiveIn |= I->second.LiveOut;
+        // PR37130: transformations prior to stack coloring can
+        // sometimes leave behind statically unreachable blocks; these
+        // can be safely skipped here.
+        if (I != BlockLiveness.end())
+          LocalLiveIn |= I->second.LiveOut;
       }
 
       // Compute LiveOut by subtracting out lifetimes that end in this