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

[Chris Lattner]

Changes in directory llvm/lib/CodeGen:

BranchFolding.cpp updated: 1.16 -> 1.17
---
Log message:

Transform code like:

  jle FOO
  jmp BAR
BAR:

into:

  jle FOO
BAR:

... whoa!



---
Diffs of the changes:  (+13 -2)

 BranchFolding.cpp |   15 +++++++++++++--
 1 files changed, 13 insertions(+), 2 deletions(-)


Index: llvm/lib/CodeGen/BranchFolding.cpp
diff -u llvm/lib/CodeGen/BranchFolding.cpp:1.16 llvm/lib/CodeGen/BranchFolding.cpp:1.17
--- llvm/lib/CodeGen/BranchFolding.cpp:1.16	Sat Oct 21 00:08:28 2006
+++ llvm/lib/CodeGen/BranchFolding.cpp	Sat Oct 21 00:43:30 2006
@@ -30,7 +30,7 @@
 static Statistic<> NumDeadBlocks("branchfold", "Number of dead blocks removed");
 static Statistic<> NumBranchOpts("branchfold", "Number of branches optimized");
 static Statistic<> NumTailMerge ("branchfold", "Number of block tails merged");
-static cl::opt<bool> EnableTailMerge("enable-tail-merge");
+static cl::opt<bool> EnableTailMerge("enable-tail-merge", cl::init(false));
 
 namespace {
   struct BranchFolder : public MachineFunctionPass {
@@ -442,7 +442,8 @@
                                        !PriorCond.empty(), MBB);
     
     // If the previous branch is conditional and both conditions go to the same
-    // destination, remove the branch, replacing it with an unconditional one.
+    // destination, remove the branch, replacing it with an unconditional one or
+    // a fall-through.
     if (PriorTBB && PriorTBB == PriorFBB) {
       TII->RemoveBranch(PrevBB);
       PriorCond.clear(); 
@@ -461,6 +462,16 @@
       ++NumBranchOpts;
       return OptimizeBlock(MBB);
     }
+    
+    // If the prior block branches somewhere else on the condition and here if
+    // the condition is false, remove the uncond second branch.
+    if (PriorFBB == &*MBB) {
+      TII->RemoveBranch(PrevBB);
+      TII->InsertBranch(PrevBB, PriorTBB, 0, PriorCond);
+      MadeChange = true;
+      ++NumBranchOpts;
+      return OptimizeBlock(MBB);
+    }
   }
   
   // Analyze the branch in the current block.