[InstCombine] Don't look at ConstantData users

When looking at PHI operand for combining, only look at instructions and
arguments. The loop later iteraters over Arg's users, which is not
useful if Arg is a constant -- it's users are not meaningful and might
be in different functions, which causes problems for the dominates()
query.

Pull Request: #103302

Author: aengelke

llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp

@@ -143,6 +143,10 @@ bool InstCombinerImpl::foldIntegerTypedPHI(PHINode &PN) {
     BasicBlock *BB = std::get<0>(Incoming);
     Value *Arg = std::get<1>(Incoming);
 
+    // Arg could be a constant, constant expr, etc., which we don't cover here.
+    if (!isa<Instruction>(Arg) && !isa<Argument>(Arg))
+      return false;
+
     // First look backward:
     if (auto *PI = dyn_cast<PtrToIntInst>(Arg)) {
       AvailablePtrVals.emplace_back(PI->getOperand(0));

llvm/test/Transforms/InstCombine/phi-int-users.ll

@@ -0,0 +1,44 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S < %s -passes=instcombine | FileCheck %s
+
+; Verify that instcombine doesn't look at users of Constant in different
+; functions for dominates() queries.
+
+define void @f1(i1 %a) {
+; CHECK-LABEL: define void @f1(
+; CHECK-SAME: i1 [[A:%.*]]) {
+; CHECK-NEXT:    br label %[[BB1:.*]]
+; CHECK:       [[BB1]]:
+; CHECK-NEXT:    br i1 [[A]], label %[[BB3:.*]], label %[[BB2:.*]]
+; CHECK:       [[BB2]]:
+; CHECK-NEXT:    br label %[[BB3]]
+; CHECK:       [[BB3]]:
+; CHECK-NEXT:    [[PHI:%.*]] = phi i64 [ 0, %[[BB2]] ], [ 1, %[[BB1]] ]
+; CHECK-NEXT:    [[INTTOPTR:%.*]] = inttoptr i64 [[PHI]] to ptr
+; CHECK-NEXT:    store i32 0, ptr [[INTTOPTR]], align 4
+; CHECK-NEXT:    br label %[[BB1]]
+;
+  br label %bb1
+
+bb1:
+  br i1 %a, label %bb3, label %bb2
+
+bb2:
+  br label %bb3
+
+bb3:
+  %phi = phi i64 [ 0, %bb2 ], [ 1, %bb1 ]
+  %inttoptr = inttoptr i64 %phi to ptr
+  store i32 0, ptr %inttoptr, align 4
+  br label %bb1
+}
+
+define void @f2() {
+; CHECK-LABEL: define void @f2() {
+; CHECK-NEXT:  [[BB:.*:]]
+; CHECK-NEXT:    ret void
+;
+bb:
+  %inttoptr = inttoptr i64 0 to ptr
+  ret void
+}