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[Attributor] Manifest constant return values 

Summary:
If the unique return value is a constant we now replace call uses with
that constant.

Reviewers: sstefan1, uenoku

Subscribers: hiraditya, bollu, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66551

llvm-svn: 369785
This commit is contained in:
Johannes Doerfert 2019-08-23 17:41:37 +00:00
parent 785fad3202
commit 23400e618b
2 changed files with 34 additions and 1 deletions
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26
llvm/lib/Transforms/IPO/Attributor.cpp
View File

@ -807,10 +807,34 @@ ChangeStatus AAReturnedValuesImpl::manifest(Attributor &A) {
STATS_DECLTRACK(UniqueReturnValue, FunctionReturn,
"Number of function with unique return");
// Callback to replace the uses of CB with the constant C.
auto ReplaceCallSiteUsersWith = [](CallBase &CB, Constant &C) {
if (CB.getNumUses() == 0)
return ChangeStatus::UNCHANGED;
CB.replaceAllUsesWith(&C);
return ChangeStatus::CHANGED;
};
// If the assumed unique return value is an argument, annotate it.
if (auto *UniqueRVArg = dyn_cast<Argument>(UniqueRV.getValue())) {
getIRPosition() = IRPosition::argument(*UniqueRVArg);
Changed = IRAttribute::manifest(A) | Changed;
Changed = IRAttribute::manifest(A);
} else if (auto *RVC = dyn_cast<Constant>(UniqueRV.getValue())) {
// We can replace the returned value with the unique returned constant.
Value &AnchorValue = getAnchorValue();
if (Function *F = dyn_cast<Function>(&AnchorValue)) {
for (const Use &U : F->uses())
if (CallBase *CB = dyn_cast<CallBase>(U.getUser()))
if (CB->isCallee(&U))
Changed = ReplaceCallSiteUsersWith(*CB, *RVC) | Changed;
} else {
assert(isa<CallBase>(AnchorValue) &&
"Expcected a function or call base anchor!");
Changed = ReplaceCallSiteUsersWith(cast<CallBase>(AnchorValue), *RVC);
}
if (Changed == ChangeStatus::CHANGED)
STATS_DECLTRACK(UniqueConstantReturnValue, FunctionReturn,
"Number of function returns replaced by constant return");
}
return Changed;

9
llvm/test/Transforms/FunctionAttrs/nounwind.ll
View File

@ -92,6 +92,15 @@ define i32 @catch_thing() personality i8* bitcast (i32 (...)* @__gxx_personality
ret i32 -1
}
define i32 @catch_thing_user() {
; ATTRIBUTOR: define i32 @catch_thing_user
; ATTRIBUTOR-NEXT: %catch_thing_call = call
; ATTRIBUTOR-NEXT: ret i32 -1
%catch_thing_call = call i32 @catch_thing()
ret i32 %catch_thing_call
}
declare i32 @__gxx_personality_v0(...)
declare i8* @__cxa_begin_catch(i8*)