[llvm] r297186 - [JumpThread] Simplify CmpInst-as-Condition branch-folding a bit.

[Xin Tong via llvm-commits]

Author: trentxintong
Date: Tue Mar  7 12:59:09 2017
New Revision: 297186

URL: http://llvm.org/viewvc/llvm-project?rev=297186&view=rev
Log:
[JumpThread] Simplify CmpInst-as-Condition branch-folding a bit.

Summary: Simplify CmpInst-as-Condition branch-folding a bit.

Reviewers: sanjoy, efriedma

Reviewed By: efriedma

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D30429

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=297186&r1=297185&r2=297186&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp Tue Mar  7 12:59:09 2017
@@ -808,7 +808,12 @@ bool JumpThreadingPass::ProcessBlock(Bas
     // TODO: This should be extended to handle switches as well.
     BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
     Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1));
-    if (CondBr && CondConst && CondBr->isConditional()) {
+    if (CondBr && CondConst) {
+      // We should have returned as soon as we turn a conditional branch to
+      // unconditional. Because its no longer interesting as far as jump
+      // threading is concerned.
+      assert(CondBr->isConditional() && "Threading on unconditional terminator");
+
       LazyValueInfo::Tristate Ret =
         LVI->getPredicateAt(CondCmp->getPredicate(), CondCmp->getOperand(0),
                             CondConst, CondBr);
@@ -831,10 +836,12 @@ bool JumpThreadingPass::ProcessBlock(Bas
         }
         return true;
       }
-    }
 
-    if (CondBr && CondConst && TryToUnfoldSelect(CondCmp, BB))
-      return true;
+      // We did not manage to simplify this branch, try to see whether
+      // CondCmp depends on a known phi-select pattern.
+      if (TryToUnfoldSelect(CondCmp, BB))
+        return true;
+    }
   }
 
   // Check for some cases that are worth simplifying.  Right now we want to look