[ConstantRange] Make getEquivalentICmp smarter

This change teaches getEquivalentICmp to be smarter about generating
ICMP_NE and ICMP_EQ predicates.

An earlier version of this change was landed as rL283057 which had a
use-after-free bug.  This new version has a fix for that bug, and a (C++
unittests/) test case that would have triggered it rL283057.

llvm-svn: 283078

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index 0f5c7128f3d..b422eea3692 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -147,6 +147,14 @@ bool ConstantRange::getEquivalentICmp(CmpInst::Predicate &Pred,
     Pred = isEmptySet() ? CmpInst::ICMP_ULT : CmpInst::ICMP_UGE;
     RHS = APInt(getBitWidth(), 0);
     Success = true;
+  } else if (auto *OnlyElt = getSingleElement()) {
+    Pred = CmpInst::ICMP_EQ;
+    RHS = *OnlyElt;
+    Success = true;
+  } else if (auto *OnlyMissingElt = getSingleMissingElement()) {
+    Pred = CmpInst::ICMP_NE;
+    RHS = *OnlyMissingElt;
+    Success = true;
   } else if (getLower().isMinSignedValue() || getLower().isMinValue()) {
     Pred =
         getLower().isMinSignedValue() ? CmpInst::ICMP_SLT : CmpInst::ICMP_ULT;