llvm-reduce: Fix asserting on TargetExtTypes that do not support zeroinit (#132733)

So far I've been unsuccessful in finding an example where the used constant
value is directly observed in the output. This avoids an assert in an intermediate
step of value replacement.

Author: arsenm

llvm/test/tools/llvm-reduce/operands-to-args-target-ext-type.ll

@@ -0,0 +1,32 @@
+; RUN: llvm-reduce %s -o %t --abort-on-invalid-reduction --delta-passes=operands-to-args --test FileCheck --test-arg %s --test-arg --check-prefixes=INTERESTING --test-arg --input-file
+; RUN: FileCheck %s --input-file %t --check-prefixes=RESULT
+
+; Make sure there's no assert from trying to create a
+; not-zeroinitializable target ext type
+
+
+declare void @uses_ext_ty(target("sometarget.sometype"))
+declare target("sometarget.sometype") @produces_ext_ty()
+
+; INTERESTING: define void @not_zero_foldable(
+
+; RESULT: define void @not_zero_foldable(target("sometarget.sometype") %call) {
+; RESULT-NEXT: %call1 = call target("sometarget.sometype") @produces_ext_ty()
+; RESULT-NEXT: call void @uses_ext_ty(target("sometarget.sometype") %call)
+define void @not_zero_foldable() {
+  %call = call target("sometarget.sometype") @produces_ext_ty()
+  call void @uses_ext_ty(target("sometarget.sometype") %call)
+  ret void
+}
+
+declare void @uses_zeroinit_ext_ty(target("spirv.zeroinit"))
+declare target("sometarget.sometype") @produces_zeroinit_ext_ty()
+
+; INTERESTING: define void @foldable_to_zero(
+; RESULT: define void @foldable_to_zero(target("spirv.zeroinit") %call) {
+define void @foldable_to_zero() {
+  %call = call target("spirv.zeroinit") @produces_zeroinit_ext_ty()
+  call void @uses_zeroinit_ext_ty(target("spirv.zeroinit") %call)
+  ret void
+}
+

llvm/test/tools/llvm-reduce/reduce-args-target-ext-ty.ll

@@ -0,0 +1,13 @@
+; RUN: llvm-reduce %s -o %t --abort-on-invalid-reduction --delta-passes=arguments --test FileCheck --test-arg %s --test-arg --check-prefixes=INTERESTING --test-arg --input-file
+; RUN: FileCheck %s --input-file %t --check-prefixes=RESULT
+
+declare void @uses_ext_ty(target("sometarget.sometype"))
+declare target("sometarget.sometype") @produces_ext_ty()
+
+; INTERESTING: @interesting(
+; RESULT: @interesting(
+; RESULT: void @uses_ext_ty()
+define void @interesting(target("sometarget.sometype") %arg) {
+  call void @uses_ext_ty(target("sometarget.sometype") %arg)
+  ret void
+}

llvm/tools/llvm-reduce/deltas/Utils.cpp

@@ -24,7 +24,16 @@ cl::opt<bool> llvm::Verbose("verbose",
                             cl::init(false), cl::cat(LLVMReduceOptions));
 
 Value *llvm::getDefaultValue(Type *T) {
-  return T->isVoidTy() ? PoisonValue::get(T) : Constant::getNullValue(T);
+  if (T->isVoidTy())
+    return PoisonValue::get(T);
+
+  if (auto *TET = dyn_cast<TargetExtType>(T)) {
+    if (TET->hasProperty(TargetExtType::HasZeroInit))
+      return ConstantTargetNone::get(TET);
+    return PoisonValue::get(TET);
+  }
+
+  return Constant::getNullValue(T);
 }
 
 bool llvm::hasAliasUse(Function &F) {