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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73768 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index ed84ec1..5a70fc3 100644
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -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