[LVI] Check for @llvm.assume dominating the edge branch

When LazyValueInfo uses @llvm.assume intrinsics to provide edge-value
constraints, we should check for intrinsics that dominate the edge's branch,
not just any potential context instructions. An assumption that dominates the
edge's branch represents a truth on that edge. This is specifically useful, for
example, if multiple predecessors assume a pointer to be nonnull, allowing us
to simplify a later null comparison.

The test case, and an initial patch, were provided by Philip Reames. Thanks!

llvm-svn: 219688

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index 7ee35b212d3..ec2c798e6c6 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -954,6 +954,7 @@ bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
 
     // Try to intersect ranges of the BB and the constraint on the edge.
     LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
+    mergeAssumeBlockValueConstantRange(Val, InBlock, BBFrom->getTerminator());
     mergeAssumeBlockValueConstantRange(Val, InBlock, CxtI);
     if (!InBlock.isConstantRange())
       return true;
@@ -971,6 +972,7 @@ bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
 
   // if we couldn't compute the value on the edge, use the value from the BB
   Result = getBlockValue(Val, BBFrom);
+  mergeAssumeBlockValueConstantRange(Val, Result, BBFrom->getTerminator());
   mergeAssumeBlockValueConstantRange(Val, Result, CxtI);
   return true;
 }