[llvm-commits] CVS: llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

[Chris Lattner]

Changes in directory llvm/lib/CodeGen/SelectionDAG:

SelectionDAGISel.cpp updated: 1.294 -> 1.295
---
Log message:

Minor tweak.  Instead of generating:

        movl 32(%esp), %eax
        cmpl $1, %eax
        je LBB1_1       #bb
LBB1_4: #entry
        cmpl $2, %eax
        je LBB1_2       #bb2
        jmp LBB1_3      #UnifiedReturnBlock
LBB1_1: #bb

notice that we would miss the fall through and emit this instead:

        movl 32(%esp), %eax
        cmpl $2, %eax
        je LBB1_2       #bb2
LBB1_4: #entry
        cmpl $1, %eax
        jne LBB1_3      #UnifiedReturnBlock
LBB1_1: #bb




---
Diffs of the changes:  (+13 -0)

 SelectionDAGISel.cpp |   13 +++++++++++++
 1 files changed, 13 insertions(+)


Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
diff -u llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:1.294 llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:1.295
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:1.294	Sun Oct 22 18:00:53 2006
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp	Mon Oct 23 13:38:22 2006
@@ -936,6 +936,19 @@
     // use bit manipulation to do two compares at once.  For example:
     // "if (X == 6 || X == 4)" -> "if ((X|2) == 6)"
     
+    // Rearrange the case blocks so that the last one falls through if possible.
+    if (NextBlock && Default != NextBlock && Cases.back().second != NextBlock) {
+      // The last case block won't fall through into 'NextBlock' if we emit the
+      // branches in this order.  See if rearranging a case value would help.
+      for (unsigned i = 0, e = Cases.size()-1; i != e; ++i) {
+        if (Cases[i].second == NextBlock) {
+          std::swap(Cases[i], Cases.back());
+          break;
+        }
+      }
+    }
+    
+    
     // Create a CaseBlock record representing a conditional branch to
     // the Case's target mbb if the value being switched on SV is equal
     // to C.