[IR] Intersect call and fn range in CallBase::getRange()

To make sure that a larger range on the call-site does not suppress
information from a smaller range at the declaration.

Author: nikic

llvm/lib/IR/Instructions.cpp

@@ -376,9 +376,17 @@ FPClassTest CallBase::getParamNoFPClass(unsigned i) const {
 }
 
 std::optional<ConstantRange> CallBase::getRange() const {
-  const Attribute RangeAttr = getRetAttr(llvm::Attribute::Range);
-  if (RangeAttr.isValid())
-    return RangeAttr.getRange();
+  Attribute CallAttr = Attrs.getRetAttr(Attribute::Range);
+  Attribute FnAttr;
+  if (const Function *F = getCalledFunction())
+    FnAttr = F->getRetAttribute(Attribute::Range);
+
+  if (CallAttr.isValid() && FnAttr.isValid())
+    return CallAttr.getRange().intersectWith(FnAttr.getRange());
+  if (CallAttr.isValid())
+    return CallAttr.getRange();
+  if (FnAttr.isValid())
+    return FnAttr.getRange();
   return std::nullopt;
 }
 

llvm/test/Transforms/CorrelatedValuePropagation/uscmp.ll

@@ -312,11 +312,9 @@ define i8 @ucmp_switch_callsite_range(i32 %x, i32 %y) {
 ; CHECK-LABEL: @ucmp_switch_callsite_range(
 ; CHECK-NEXT:    [[CMP:%.*]] = call range(i8 -2, 3) i8 @llvm.ucmp.i8.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
 ; CHECK-NEXT:    switch i8 [[CMP]], label [[DEFAULT_UNREACHABLE:%.*]] [
-; CHECK-NEXT:      i8 -2, label [[BB_NEG2:%.*]]
+; CHECK-NEXT:      i8 1, label [[BB_1:%.*]]
 ; CHECK-NEXT:      i8 -1, label [[BB_NEG1:%.*]]
 ; CHECK-NEXT:      i8 0, label [[BB_0:%.*]]
-; CHECK-NEXT:      i8 1, label [[BB_1:%.*]]
-; CHECK-NEXT:      i8 2, label [[BB_2:%.*]]
 ; CHECK-NEXT:    ]
 ; CHECK:       bb.neg2:
 ; CHECK-NEXT:    ret i8 -2