[llvm-commits] [llvm] r94321 - in /llvm/trunk: lib/Transforms/Scalar/JumpThreading.cpp test/Transforms/JumpThreading/crash.ll

[Chris Lattner]

Author: lattner
Date: Sat Jan 23 13:16:25 2010
New Revision: 94321

URL: http://llvm.org/viewvc/llvm-project?rev=94321&view=rev
Log:
add an early out to ProcessBranchOnXOR to speed it up,
handle the case when we can infer an input to the xor
from all inputs that agree, instead of going into an
infinite loop.  Another part of PR6199

Modified:
    llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
    llvm/trunk/test/Transforms/JumpThreading/crash.ll

Modified: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp?rev=94321&r1=94320&r2=94321&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp Sat Jan 23 13:16:25 2010
@@ -1123,6 +1123,11 @@
       isa<ConstantInt>(BO->getOperand(1)))
     return false;
   
+  // If the first instruction in BB isn't a phi, we won't be able to infer
+  // anything special about any particular predecessor.
+  if (!isa<PHINode>(BB->front()))
+    return false;
+  
   // If we have a xor as the branch input to this block, and we know that the
   // LHS or RHS of the xor in any predecessor is true/false, then we can clone
   // the condition into the predecessor and fix that value to true, saving some
@@ -1180,6 +1185,26 @@
     BlocksToFoldInto.push_back(XorOpValues[i].second);
   }
   
+  // If we inferred a value for all of the predecessors, then duplication won't
+  // help us.  However, we can just replace the LHS or RHS with the constant.
+  if (BlocksToFoldInto.size() ==
+      cast<PHINode>(BB->front()).getNumIncomingValues()) {
+    if (SplitVal == 0) {
+      // If all preds provide undef, just nuke the xor, because it is undef too.
+      BO->replaceAllUsesWith(UndefValue::get(BO->getType()));
+      BO->eraseFromParent();
+    } else if (SplitVal->isZero()) {
+      // If all preds provide 0, replace the xor with the other input.
+      BO->replaceAllUsesWith(BO->getOperand(isLHS));
+      BO->eraseFromParent();
+    } else {
+      // If all preds provide 1, set the computed value to 1.
+      BO->setOperand(!isLHS, SplitVal);
+    }
+    
+    return true;
+  }
+  
   // Try to duplicate BB into PredBB.
   return DuplicateCondBranchOnPHIIntoPred(BB, BlocksToFoldInto);
 }

Modified: llvm/trunk/test/Transforms/JumpThreading/crash.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/JumpThreading/crash.ll?rev=94321&r1=94320&r2=94321&view=diff

==============================================================================
--- llvm/trunk/test/Transforms/JumpThreading/crash.ll (original)
+++ llvm/trunk/test/Transforms/JumpThreading/crash.ll Sat Jan 23 13:16:25 2010
@@ -259,3 +259,30 @@
 for.body:                                         ; preds = %for.cond
   br label %for.cond
 }
+
+; PR6119
+define i32 @test9(i32 %action) nounwind {
+entry:
+  switch i32 %action, label %lor.rhs [
+    i32 1, label %if.then
+    i32 0, label %lor.end
+  ]
+
+if.then:                                          ; preds = %for.cond, %lor.end, %entry
+  ret i32 undef
+
+lor.rhs:                                          ; preds = %entry
+  br label %lor.end
+
+lor.end:                                          ; preds = %lor.rhs, %entry
+  %0 = phi i1 [ undef, %lor.rhs ], [ true, %entry ] ; <i1> [#uses=1]
+  %cmp103 = xor i1 undef, %0                      ; <i1> [#uses=1]
+  br i1 %cmp103, label %for.cond, label %if.then
+
+for.cond:                                         ; preds = %for.body, %lor.end
+  br i1 undef, label %if.then, label %for.body
+
+for.body:                                         ; preds = %for.cond
+  br label %for.cond
+}
+