Add handling for range metadata in ValueTracking isKnownNonZero

If we load from a location with range metadata, we can use information about the ranges of the loaded value for optimization purposes.  This helps to remove redundant checks and canonicalize checks for other optimization passes.  This particular patch checks whether a value is known to be non-zero from the range metadata.

Currently, these tests are against InstCombine.  In theory, all of these should be InstSimplify since we're not inserting any new instructions.  Moving the code may follow in a separate change.

Reviewed by: Hal
Differential Revision: http://reviews.llvm.org/D5947

llvm-svn: 220925

1 files changed, 29 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 87a6b83..da5ba0b 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -1502,6 +1502,23 @@ static bool isGEPKnownNonNull(GEPOperator *GEP, const DataLayout *DL,
   return false;
 }
 
+/// Does the 'Range' metadata (which must be a valid MD_range operand list)
+/// ensure that the value it's attached to is never Value?  'RangeType' is
+/// is the type of the value described by the range.
+static bool rangeMetadataExcludesValue(MDNode* Ranges,
+                                       const APInt& Value) {
+  const unsigned NumRanges = Ranges->getNumOperands() / 2;
+  assert(NumRanges >= 1);
+  for (unsigned i = 0; i < NumRanges; ++i) {
+    ConstantInt *Lower = cast<ConstantInt>(Ranges->getOperand(2*i + 0));
+    ConstantInt *Upper = cast<ConstantInt>(Ranges->getOperand(2*i + 1));
+    ConstantRange Range(Lower->getValue(), Upper->getValue());
+    if (Range.contains(Value))
+      return false;
+  }
+  return true;
+}
+
 /// isKnownNonZero - Return true if the given value is known to be non-zero
 /// when defined.  For vectors return true if every element is known to be
 /// non-zero when defined.  Supports values with integer or pointer type and
@@ -1518,6 +1535,18 @@ bool isKnownNonZero(Value *V, const DataLayout *TD, unsigned Depth,
     return false;
   }
 
+  if (Instruction* I = dyn_cast<Instruction>(V)) {
+    if (MDNode *Ranges = I->getMetadata(LLVMContext::MD_range)) {
+      // If the possible ranges don't contain zero, then the value is
+      // definitely non-zero.
+      if (IntegerType* Ty = dyn_cast<IntegerType>(V->getType())) {
+        const APInt ZeroValue(Ty->getBitWidth(), 0);
+        if (rangeMetadataExcludesValue(Ranges, ZeroValue))
+          return true;
+      }
+    }
+  }
+
   // The remaining tests are all recursive, so bail out if we hit the limit.
   if (Depth++ >= MaxDepth)
     return false;