[llvm-commits] [llvm] r101165 - /llvm/trunk/lib/CodeGen/MachineSink.cpp

[Jakob Stoklund Olesen]

Author: stoklund
Date: Tue Apr 13 14:06:14 2010
New Revision: 101165

URL: http://llvm.org/viewvc/llvm-project?rev=101165&view=rev
Log:
Teach MachineSinking to handle easy critical edges.

Sometimes it is desirable to sink instructions along a critical edge:

x = ...
if (a && b) ...
else use(x);

The 'a && b' condition creates a critical edge to the else block, but we still
want to sink the computation of x into the block. The else block is dominated by
the parent block, so we are not pushing instructions into new code paths.

Modified:
    llvm/trunk/lib/CodeGen/MachineSink.cpp

Modified: llvm/trunk/lib/CodeGen/MachineSink.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineSink.cpp?rev=101165&r1=101164&r2=101165&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineSink.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineSink.cpp Tue Apr 13 14:06:14 2010
@@ -276,8 +276,23 @@
   // but for now we just punt.
   // FIXME: Split critical edges if not backedges.
   if (SuccToSinkTo->pred_size() > 1) {
-    DEBUG(dbgs() << " *** PUNTING: Critical edge found\n");
-    return false;
+    // We cannot sink a load across a critical edge - there may be stores in
+    // other code paths.
+    bool store = true;
+    if (!MI->isSafeToMove(TII, AA, store)) {
+      DEBUG(dbgs() << " *** PUNTING: Wont sink load along critical edge.\n");
+      return false;
+    }
+
+    // We don't want to sink across a critical edge if we don't dominate the
+    // successor. We could be introducing calculations to new code paths.
+    if (!DT->dominates(ParentBlock, SuccToSinkTo)) {
+      DEBUG(dbgs() << " *** PUNTING: Critical edge found\n");
+      return false;
+    }
+
+    // Otherwise we are OK with sinking along a critical edge.
+    DEBUG(dbgs() << "Sinking along critical edge.\n");
   }
   
   // Determine where to insert into.  Skip phi nodes.