[LVI/CVP] Teach LVI about range metadata

Somewhat shockingly for an analysis pass which is computing constant ranges, LVI did not understand the ranges provided by range metadata.

As part of this change, I included a change to CVP primarily because doing so made it much easier to write small self contained test cases. CVP was previously only handling the non-local operand case, but given that LVI can sometimes figure out information about instructions standalone, I don't see any reason to restrict this.  There could possibly be a compile time impact from this, but I suspect it should be minimal.  If anyone has an example which substaintially regresses, please let me know.  I could restrict the block local handling to ICmps feeding Terminator instructions if needed.  

Note that this patch continues a somewhat bad practice in LVI. In many cases, we know facts about values, and separate context sensitive facts about values. LVI makes no effort to distinguish and will frequently cache the same value fact repeatedly for different contexts. I would like to change this, but that's a large enough change that I want it to go in separately with clear documentation of what's changing. Other examples of this include the non-null handling, and arguments.

As a meta comment: the entire motivation of this change was being able to write smaller (aka reasonable sized) test cases for a future patch teaching LVI about select instructions.

Differential Revision: http://reviews.llvm.org/D13543

llvm-svn: 251606

1 files changed, 6 insertions, 26 deletions

diff --git a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
index e6acbdf1602..12944142f5c 100644
--- a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
+++ b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
@@ -181,44 +181,24 @@ bool CorrelatedValuePropagation::processMemAccess(Instruction *I) {
   return true;
 }
 
-/// processCmp - If the value of this comparison could be determined locally,
-/// constant propagation would already have figured it out.  Instead, walk
-/// the predecessors and statically evaluate the comparison based on information
-/// available on that edge.  If a given static evaluation is true on ALL
-/// incoming edges, then it's true universally and we can simplify the compare.
+/// processCmp - See if LazyValueInfo's ability to exploit edge conditions,
+/// or range information is sufficient to prove this comparison.  Even for
+/// local conditions, this can sometimes prove conditions instcombine can't by
+/// exploiting range information.
 bool CorrelatedValuePropagation::processCmp(CmpInst *C) {
   Value *Op0 = C->getOperand(0);
-  if (isa<Instruction>(Op0) &&
-      cast<Instruction>(Op0)->getParent() == C->getParent())
-    return false;
-
   Constant *Op1 = dyn_cast<Constant>(C->getOperand(1));
   if (!Op1) return false;
 
-  pred_iterator PI = pred_begin(C->getParent()), PE = pred_end(C->getParent());
-  if (PI == PE) return false;
-
-  LazyValueInfo::Tristate Result = LVI->getPredicateOnEdge(C->getPredicate(),
-                                    C->getOperand(0), Op1, *PI,
-                                    C->getParent(), C);
+  LazyValueInfo::Tristate Result =
+    LVI->getPredicateAt(C->getPredicate(), Op0, Op1, C);
   if (Result == LazyValueInfo::Unknown) return false;
 
-  ++PI;
-  while (PI != PE) {
-    LazyValueInfo::Tristate Res = LVI->getPredicateOnEdge(C->getPredicate(),
-                                    C->getOperand(0), Op1, *PI,
-                                    C->getParent(), C);
-    if (Res != Result) return false;
-    ++PI;
-  }
-
   ++NumCmps;
-
   if (Result == LazyValueInfo::True)
     C->replaceAllUsesWith(ConstantInt::getTrue(C->getContext()));
   else
     C->replaceAllUsesWith(ConstantInt::getFalse(C->getContext()));
-
   C->eraseFromParent();
 
   return true;