Fix an assert condition in lowering.

Tail calls via the tail call helper must live in GC-safe blocks. A block
is GC-safe if either it or all of its dominators are also GC-safe. If we
are not optimizing, we will not compute dominators, and will therfore
not mark blocks whose dominators are all GC-safe. When deciding whether
or not we need to make a block GC-safe during tail call morphing,
however, we allow a tail call in an unmarked block iff the entry block
is GC-safe, as the entry block trivially dominates every reachable
block. This change fixes an assert that was not allowing for a tail call
in a block that is not marked GC-safe where the entry block is marked
GC-safe.

Commit migrated from https://github.com/dotnet/coreclr/commit/c777aec201d57ef1f896bd5a3089fb322cd53707

diff --git a/src/coreclr/src/jit/lower.cpp b/src/coreclr/src/jit/lower.cpp
index 0018ad4..c7f04f8 100644 (file)
--- a/src/coreclr/src/jit/lower.cpp
+++ b/src/coreclr/src/jit/lower.cpp
@@ -1760,8 +1760,10 @@ GenTree* Lowering::LowerTailCallViaHelper(GenTreeCall* call, GenTree* callTarget
 
     // The TailCall helper call never returns to the caller and is not GC interruptible.
     // Therefore the block containing the tail call should be a GC safe point to avoid
-    // GC starvation.
-    assert(comp->compCurBB->bbFlags & BBF_GC_SAFE_POINT);
+    // GC starvation. It is legal for the block to be unmarked iff the entry block is a
+    // GC safe point, as the entry block trivially dominates every reachable block.
+    assert((comp->compCurBB->bbFlags & BBF_GC_SAFE_POINT) || (comp->fgFirstBB->bbFlags & BBF_GC_SAFE_POINT));
+
 
     // If PInvokes are in-lined, we have to remember to execute PInvoke method epilog anywhere that
     // a method returns.  This is a case of caller method has both PInvokes and tail calls.