[llvm-commits] [llvm] r73768 - in /llvm/trunk: lib/Transforms/Scalar/JumpThreading.cpp test/Transforms/JumpThreading/dup-cond.ll

[Chris Lattner]

Author: lattner
Date: Fri Jun 19 11:27:56 2009
New Revision: 73768

URL: http://llvm.org/viewvc/llvm-project?rev=73768&view=rev
Log:
make jump threading handle lexically identical compare instructions
as if they were multiple uses of the same instruction.  This interacts
well with the existing loadpre that j-t does to open up many new jump
threads earlier.

Added:
    llvm/trunk/test/Transforms/JumpThreading/dup-cond.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp?rev=73768&r1=73767&r2=73768&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp Fri Jun 19 11:27:56 2009
@@ -324,10 +324,6 @@
     }
   }
 
-  // If there is only a single predecessor of this block, nothing to fold.
-  if (BB->getSinglePredecessor())
-    return false;
-  
   // All the rest of our checks depend on the condition being an instruction.
   if (CondInst == 0)
     return false;
@@ -358,6 +354,23 @@
       if (ProcessBranchOnCompare(CondCmp, BB))
         return true;      
     }
+    
+    // If we have a comparison, loop over the predecessors to see if there is
+    // a condition with the same value.
+    pred_iterator PI = pred_begin(BB), E = pred_end(BB);
+    for (; PI != E; ++PI)
+      if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
+        if (PBI->isConditional() && *PI != BB) {
+          if (CmpInst *CI = dyn_cast<CmpInst>(PBI->getCondition())) {
+            if (CI->getOperand(0) == CondCmp->getOperand(0) &&
+                CI->getOperand(1) == CondCmp->getOperand(1) &&
+                CI->getPredicate() == CondCmp->getPredicate()) {
+              // TODO: Could handle things like (x != 4) --> (x == 17)
+              if (ProcessBranchOnDuplicateCond(*PI, BB))
+                return true;
+            }
+          }
+        }
   }
 
   // Check for some cases that are worth simplifying.  Right now we want to look

Added: llvm/trunk/test/Transforms/JumpThreading/dup-cond.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/JumpThreading/dup-cond.ll?rev=73768&view=auto

==============================================================================
--- llvm/trunk/test/Transforms/JumpThreading/dup-cond.ll (added)
+++ llvm/trunk/test/Transforms/JumpThreading/dup-cond.ll Fri Jun 19 11:27:56 2009
@@ -0,0 +1,30 @@
+; RUN: llvm-as < %s | opt -jump-threading -die | llvm-dis | grep icmp | count 1
+
+declare void @f1()
+declare void @f2()
+declare void @f3()
+
+define i32 @test(i32 %A) {
+	%tmp455 = icmp eq i32 %A, 42
+	br i1 %tmp455, label %BB1, label %BB2
+        
+BB2:
+	call void @f1()
+	br label %BB1
+        
+
+BB1:
+	%tmp459 = icmp eq i32 %A, 42
+	br i1 %tmp459, label %BB3, label %BB4
+
+BB3:
+	call void @f2()
+        ret i32 3
+
+BB4:
+	call void @f3()
+	ret i32 4
+}
+
+
+