llvm-reduce: Change function return types if function is not called

llvm/test/tools/llvm-reduce/reduce-instructions-to-return.ll

@@ -196,13 +196,25 @@ define i32 @callsite_already_new_return_type(ptr %arg) {
 ; INTERESTING: ret
 
 ; RESULT-LABEL: define ptr @non_void_no_op(
-; RESULT: ret ptr null
+; RESULT-NEXT: %load = load i32, ptr %arg
+; RESULT-NEXT: store i32 %load, ptr @gv
+; RESULT-NEXT: ret ptr null
 define ptr @non_void_no_op(ptr %arg) {
   %load = load i32, ptr %arg
   store i32 %load, ptr @gv
   ret ptr null
 }
 
+; INTERESTING-LABEL: @non_void_no_op_caller(
+
+; RESULT-LABEL: define ptr @non_void_no_op_caller(ptr %arg) {
+; RESULT-NEXT: %call = call ptr @non_void_no_op(ptr %arg)
+; RESULT-NEXT: ret ptr %call
+define ptr @non_void_no_op_caller(ptr %arg) {
+  %call = call ptr @non_void_no_op(ptr %arg)
+  ret ptr %call
+}
+
 ; INTERESTING-LABEL: @non_void_same_type_use(
 ; INTERESTING: = load
 ; INTERESTING: ret
@@ -230,6 +242,12 @@ define i32 @non_void_bitcastable_type_use(ptr %arg) {
   ret i32 0
 }
 
+; INTERESTING-LABEL: @non_void_bitcastable_type_use_caller(
+define i32 @non_void_bitcastable_type_use_caller(ptr %arg) {
+  %ret = call i32 @non_void_bitcastable_type_use(ptr %arg)
+  ret i32 %ret
+}
+
 ; INTERESTING-LABEL: @form_return_struct(
 ; INTERESTING: = load { i32, float }
 

llvm/test/tools/llvm-reduce/reduce-values-to-return-new-return-type.ll

@@ -0,0 +1,188 @@
+; Test that llvm-reduce can move intermediate values by inserting
+; early returns when the function already has a different return type
+;
+; RUN: llvm-reduce --abort-on-invalid-reduction --delta-passes=instructions-to-return --test FileCheck --test-arg --check-prefix=INTERESTING --test-arg %s --test-arg --input-file %s -o %t
+; RUN: FileCheck --check-prefix=RESULT %s < %t
+
+
+@gv = global i32 0, align 4
+@ptr_array = global [2 x ptr] [ptr @inst_to_return_has_different_type_but_no_func_call_use,
+                               ptr @multiple_callsites_wrong_return_type]
+
+; Should rewrite this return from i64 to i32 since the function has no
+; uses.
+; INTERESTING-LABEL: @inst_to_return_has_different_type_but_no_func_call_use(
+; RESULT-LABEL: define i32 @inst_to_return_has_different_type_but_no_func_call_use(ptr %arg) {
+; RESULT-NEXT: %load = load i32, ptr %arg, align 4
+; RESULT-NEXT: ret i32 %load
+define i64 @inst_to_return_has_different_type_but_no_func_call_use(ptr %arg) {
+  %load = load i32, ptr %arg
+  store i32 %load, ptr @gv
+  ret i64 0
+}
+
+; INTERESTING-LABEL: @multiple_returns_wrong_return_type_no_callers(
+; RESULT-LABEL: define i32 @multiple_returns_wrong_return_type_no_callers(
+
+; RESULT: bb0:
+; RESULT-NEXT: %load0 = load i32,
+; RESULT-NEXT: ret i32 %load0
+
+; RESULT: bb1:
+; RESULT-NEXT: store i32 8, ptr null
+; RESULT-NEXT: ret i32 0
+define i64 @multiple_returns_wrong_return_type_no_callers(ptr %arg, i1 %cond, i64 %arg2) {
+entry:
+  br i1 %cond, label %bb0, label %bb1
+
+bb0:
+  %load0 = load i32, ptr %arg
+  store i32 %load0, ptr @gv
+  ret i64 234
+
+bb1:
+  store i32 8, ptr null
+  ret i64 %arg2
+
+bb2:
+  ret i64 34
+}
+
+; INTERESTING-LABEL: define {{.+}} @callsite_different_type_unused_0(
+
+; RESULT-LABEL: define i64 @callsite_different_type_unused_0(ptr %arg) {
+; RESULT-NEXT: %unused0 = call range(i64 99, 1024) i64 @inst_to_return_has_different_type_but_call_result_unused(ptr %arg)
+; RESULT-NEXT: ret i64 %unused0
+define void @callsite_different_type_unused_0(ptr %arg) {
+  %unused0 = call range(i64 99, 1024) i64 @inst_to_return_has_different_type_but_call_result_unused(ptr %arg)
+  %unused1 = call i64 @inst_to_return_has_different_type_but_call_result_unused(ptr null)
+  ret void
+}
+
+; TODO: Could rewrite this return from i64 to i32 since the callsite is unused.
+; INTERESTING-LABEL: define {{.+}} @inst_to_return_has_different_type_but_call_result_unused(
+; RESULT-LABEL: define i64 @inst_to_return_has_different_type_but_call_result_unused(
+; RESULT-NEXT: %load = load i32, ptr %arg
+; RESULT-NEXT: store i32 %load, ptr @gv
+; RESULT: ret i64 0
+define i64 @inst_to_return_has_different_type_but_call_result_unused(ptr %arg) {
+  %load = load i32, ptr %arg
+  store i32 %load, ptr @gv
+  ret i64 0
+}
+
+; INTERESTING-LABEL: @multiple_callsites_wrong_return_type(
+; RESULT-LABEL: define i64 @multiple_callsites_wrong_return_type(
+; RESULT: ret i64 0
+define i64 @multiple_callsites_wrong_return_type(ptr %arg) {
+  %load = load i32, ptr %arg
+  store i32 %load, ptr @gv
+  ret i64 0
+}
+
+; INTERESTING-LABEL: @unused_with_wrong_return_types(
+; RESULT-LABEL: define i64 @unused_with_wrong_return_types(
+; RESULT-NEXT: %unused0 = call i64 @multiple_callsites_wrong_return_type(ptr %arg)
+; RESULT-NEXT: ret i64 %unused0
+define void @unused_with_wrong_return_types(ptr %arg) {
+  %unused0 = call i64 @multiple_callsites_wrong_return_type(ptr %arg)
+  %unused1 = call i32 @multiple_callsites_wrong_return_type(ptr %arg)
+  %unused2 = call ptr @multiple_callsites_wrong_return_type(ptr %arg)
+  ret void
+}
+
+; INTERESTING-LABEL: @multiple_returns_wrong_return_type(
+; INTERESTING: %load0 = load i32,
+
+; RESULT-LABEL: define i32 @multiple_returns_wrong_return_type(
+; RESULT: ret i32
+; RESULT: ret i32
+; RESULT: ret i32
+define i32 @multiple_returns_wrong_return_type(ptr %arg, i1 %cond, i32 %arg2) {
+entry:
+  br i1 %cond, label %bb0, label %bb1
+
+bb0:
+  %load0 = load i32, ptr %arg
+  store i32 %load0, ptr @gv
+  ret i32 234
+
+bb1:
+  ret i32 %arg2
+
+bb2:
+  ret i32 34
+}
+
+; INTERESTING-LABEL: @call_multiple_returns_wrong_return_type(
+; RESULT-LABEL: define <2 x i32> @call_multiple_returns_wrong_return_type(
+; RESULT-NEXT: %unused = call <2 x i32> @multiple_returns_wrong_return_type(
+; RESULT-NEXT: ret <2 x i32> %unused
+define void @call_multiple_returns_wrong_return_type(ptr %arg, i1 %cond, i32 %arg2) {
+  %unused = call <2 x i32> @multiple_returns_wrong_return_type(ptr %arg, i1 %cond, i32 %arg2)
+  ret void
+}
+
+; INTERESTING-LABEL: @drop_incompatible_type_return_attrs(
+
+; RESULT-LABEL: define i32 @drop_incompatible_type_return_attrs(ptr %arg, float %arg1) {
+; RESULT-NEXT: %load = load i32, ptr %arg, align 4
+; RESULT-NEXT: ret i32 %load
+define nofpclass(nan inf) float @drop_incompatible_type_return_attrs(ptr %arg, float %arg1) {
+  %load = load i32, ptr %arg
+  store i32 %load, ptr @gv
+  ret float %arg1
+}
+
+; INTERESTING-LABEL: @drop_incompatible_return_range(
+; RESULT-LABEL: define i32 @drop_incompatible_return_range(ptr %arg, i64 %arg1) {
+; RESULT-NEXT: %load = load i32, ptr %arg, align 4
+; RESULT-NEXT: ret i32 %load
+define range(i64 8, 256) i64 @drop_incompatible_return_range(ptr %arg, i64 %arg1) {
+  %load = load i32, ptr %arg
+  store i32 %load, ptr @gv
+  ret i64 %arg1
+}
+
+; INTERESTING-LABEL: @preserve_compatible_return_range(
+; RESULT-LABEL: define range(i32 8, 256) i32 @preserve_compatible_return_range(ptr %arg, <2 x i32> %arg1) {
+; RESULT-NEXT: %load = load i32, ptr %arg, align 4
+; RESULT-NEXT: ret i32 %load
+define range(i32 8, 256) <2 x i32> @preserve_compatible_return_range(ptr %arg, <2 x i32> %arg1) {
+  %load = load i32, ptr %arg
+  store i32 %load, ptr @gv
+  ret <2 x i32> %arg1
+}
+
+; INTERESTING-LABEL: @drop_incompatible_returned_param_attr_0(
+
+; RESULT-LABEL: define i32 @drop_incompatible_returned_param_attr_0(ptr %arg, ptr %arg1) {
+; RESULT-NEXT: %load = load i32, ptr %arg
+; RESULT-NEXT: ret i32 %load
+define ptr @drop_incompatible_returned_param_attr_0(ptr returned %arg, ptr %arg1) {
+  %load = load i32, ptr %arg
+  store i32 %load, ptr @gv
+  ret ptr %arg
+}
+
+; INTERESTING-LABEL: @drop_incompatible_returned_param_attr_1(
+
+; RESULT-LABEL: define i32 @drop_incompatible_returned_param_attr_1(ptr %arg, ptr %arg1) {
+; RESULT-NEXT: %load = load i32, ptr %arg
+; RESULT-NEXT: ret i32 %load
+define ptr @drop_incompatible_returned_param_attr_1(ptr %arg, ptr returned %arg1) {
+  %load = load i32, ptr %arg
+  store i32 %load, ptr @gv
+  ret ptr %arg
+}
+
+; INTERESTING-LABEL: @drop_incompatible_returned_param_attr_2
+
+; RESULT-LABEL: define ptr @drop_incompatible_returned_param_attr_2(ptr %arg, ptr %arg1) {
+; RESULT-NEXT: %load = load ptr, ptr %arg
+; RESULT-NEXT: ret ptr %load
+define ptr @drop_incompatible_returned_param_attr_2(ptr %arg, ptr returned %arg1) {
+  %load = load ptr, ptr %arg
+  store ptr %load, ptr @gv
+  ret ptr %arg1
+}

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

@@ -18,6 +18,8 @@
 
 #include "Delta.h"
 #include "Utils.h"
+#include "llvm/IR/AttributeMask.h"
+#include "llvm/IR/Attributes.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/Support/Debug.h"
@@ -55,8 +57,10 @@ static void rewriteFuncWithReturnType(Function &OldF, Value *NewRetValue) {
   BasicBlock::iterator NewValIt =
       NewRetI ? NewRetI->getIterator() : EntryBB.end();
 
-  // Hack up any return values in other blocks, we can't leave them as ret void.
-  if (OldFuncTy->getReturnType()->isVoidTy()) {
+  Type *OldRetTy = OldFuncTy->getReturnType();
+
+  // Hack up any return values in other blocks, we can't leave them as returning OldRetTy.
+  if (OldRetTy != NewRetTy) {
     for (BasicBlock &OtherRetBB : OldF) {
       if (&OtherRetBB != NewRetBlock) {
         auto *OrigRI = dyn_cast<ReturnInst>(OtherRetBB.getTerminator());
@@ -92,6 +96,18 @@ static void rewriteFuncWithReturnType(Function &OldF, Value *NewRetValue) {
   // result of our pruning here.
   EliminateUnreachableBlocks(OldF);
 
+  // Drop the incompatible attributes before we copy over to the new function.
+  if (OldRetTy != NewRetTy) {
+    AttributeList AL = OldF.getAttributes();
+    AttributeMask IncompatibleAttrs =
+        AttributeFuncs::typeIncompatible(NewRetTy, AL.getRetAttrs());
+    OldF.removeRetAttrs(IncompatibleAttrs);
+  }
+
+  // Now we need to remove any returned attributes from parameters.
+  for (Argument &A : OldF.args())
+    OldF.removeParamAttr(A.getArgNo(), Attribute::Returned);
+
   Function *NewF =
       Function::Create(NewFuncTy, OldF.getLinkage(), OldF.getAddressSpace(), "",
                        OldF.getParent());
@@ -161,7 +177,9 @@ static bool canReplaceFuncUsers(const Function &F, Type *NewRetTy) {
     if (CB->getType() == NewRetTy)
       continue;
 
-    LLVM_DEBUG(dbgs() << "Cannot replace callsite with wrong type: " << *CB
+    // TODO: If all callsites have no uses, we could mutate the type of all the
+    // callsites. This will complicate the visit and rewrite ordering though.
+    LLVM_DEBUG(dbgs() << "Cannot replace used callsite with wrong type: " << *CB
                       << '\n');
     return false;
   }
@@ -197,8 +215,7 @@ static bool shouldForwardValueToReturn(const BasicBlock &BB, const Value *V,
   if (!isReallyValidReturnType(V->getType()))
     return false;
 
-  return (RetTy->isVoidTy() ||
-          (RetTy == V->getType() && shouldReplaceNonVoidReturnValue(BB, V))) &&
+  return (RetTy->isVoidTy() || shouldReplaceNonVoidReturnValue(BB, V)) &&
          canReplaceFuncUsers(*BB.getParent(), V->getType());
 }