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[Attributor] Teach AANoCapture to use information in-flight more aggressively 

AAReturnedValues, AAMemoryBehavior, and AANoUnwind, can provide
information that helps during the tracking or even justifies no-capture.
We now use this information and enable no-capture in some test cases
designed a long while a ago for these cases.

llvm-svn: 375382
This commit is contained in:
Johannes Doerfert 2019-10-21 00:48:42 +00:00
parent e78414622d
commit 3839b57f73
6 changed files with 103 additions and 21 deletions
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71
llvm/lib/Transforms/IPO/Attributor.cpp
View File

@ -2939,7 +2939,7 @@ struct AANoCaptureImpl : public AANoCapture {
// Check what state the associated function can actually capture.
if (F)
determineFunctionCaptureCapabilities(*F, *this);
determineFunctionCaptureCapabilities(IRP, *F, *this);
else
indicatePessimisticFixpoint();
}
@ -2965,7 +2965,8 @@ struct AANoCaptureImpl : public AANoCapture {
/// Set the NOT_CAPTURED_IN_MEM and NOT_CAPTURED_IN_RET bits in \p Known
/// depending on the ability of the function associated with \p IRP to capture
/// state in memory and through "returning/throwing", respectively.
static void determineFunctionCaptureCapabilities(const Function &F,
static void determineFunctionCaptureCapabilities(const IRPosition &IRP,
const Function &F,
IntegerState &State) {
// TODO: Once we have memory behavior attributes we should use them here.
@ -2987,6 +2988,21 @@ struct AANoCaptureImpl : public AANoCapture {
// exceptions and doesn not return values.
if (F.doesNotThrow() && F.getReturnType()->isVoidTy())
State.addKnownBits(NOT_CAPTURED_IN_RET);
// Check existing "returned" attributes.
int ArgNo = IRP.getArgNo();
if (F.doesNotThrow() && ArgNo >= 0) {
for (unsigned u = 0, e = F.arg_size(); u< e; ++u)
if (F.hasParamAttribute(u, Attribute::Returned)) {
if (u == ArgNo)
State.removeAssumedBits(NOT_CAPTURED_IN_RET);
else if (F.onlyReadsMemory())
State.addKnownBits(NO_CAPTURE);
else
State.addKnownBits(NOT_CAPTURED_IN_RET);
break;
}
}
}
/// See AbstractState::getAsStr().
@ -3158,15 +3174,54 @@ ChangeStatus AANoCaptureImpl::updateImpl(Attributor &A) {
const Function *F =
getArgNo() >= 0 ? IRP.getAssociatedFunction() : IRP.getAnchorScope();
assert(F && "Expected a function!");
const auto &IsDeadAA = A.getAAFor<AAIsDead>(*this, IRPosition::function(*F));
const IRPosition &FnPos = IRPosition::function(*F);
const auto &IsDeadAA = A.getAAFor<AAIsDead>(*this, FnPos);
AANoCapture::StateType T;
// TODO: Once we have memory behavior attributes we should use them here
// similar to the reasoning in
// AANoCaptureImpl::determineFunctionCaptureCapabilities(...).
// TODO: Use the AAReturnedValues to learn if the argument can return or
// not.
// Readonly means we cannot capture through memory.
const auto &FnMemAA = A.getAAFor<AAMemoryBehavior>(*this, FnPos);
if (FnMemAA.isAssumedReadOnly()) {
T.addKnownBits(NOT_CAPTURED_IN_MEM);
if (FnMemAA.isKnownReadOnly())
addKnownBits(NOT_CAPTURED_IN_MEM);
}
// Make sure all returned values are different than the underlying value.
// TODO: we could do this in a more sophisticated way inside
// AAReturnedValues, e.g., track all values that escape through returns
// directly somehow.
auto CheckReturnedArgs = [&](const AAReturnedValues &RVAA) {
bool SeenConstant = false;
for (auto &It : RVAA.returned_values()) {
if (isa<Constant>(It.first)) {
if (SeenConstant)
return false;
SeenConstant = true;
} else if (!isa<Argument>(It.first) ||
It.first == getAssociatedArgument())
return false;
}
return true;
};
const auto &NoUnwindAA = A.getAAFor<AANoUnwind>(*this, FnPos);
if (NoUnwindAA.isAssumedNoUnwind()) {
bool IsVoidTy = F->getReturnType()->isVoidTy();
const AAReturnedValues *RVAA =
IsVoidTy ? nullptr : &A.getAAFor<AAReturnedValues>(*this, FnPos);
if (IsVoidTy || CheckReturnedArgs(*RVAA)) {
T.addKnownBits(NOT_CAPTURED_IN_RET);
if (T.isKnown(NOT_CAPTURED_IN_MEM))
return ChangeStatus::UNCHANGED;
if (NoUnwindAA.isKnownNoUnwind() &&
(IsVoidTy || RVAA->getState().isAtFixpoint())) {
addKnownBits(NOT_CAPTURED_IN_RET);
if (isKnown(NOT_CAPTURED_IN_MEM))
return indicateOptimisticFixpoint();
}
}
}
// Use the CaptureTracker interface and logic with the specialized tracker,
// defined in AACaptureUseTracker, that can look at in-flight abstract

18
llvm/test/Transforms/FunctionAttrs/arg_nocapture.ll
View File

@ -405,35 +405,33 @@ entry:
;
; Make sure the returned flag on %r is strong enough to justify nocapture on %b but **not** on %r.
;
; FIXME: The "returned" information is not propagated to the fullest extend causing us to miss "nocapture" on %b in the following:
; CHECK: define i32* @not_captured_by_readonly_call_not_returned_either1(i32* readonly %b, i32* readonly returned %r)
; CHECK: define i32* @not_captured_by_readonly_call_not_returned_either1(i32* nocapture readonly %b, i32* readonly returned %r)
;
; CHECK: define i32* @not_captured_by_readonly_call_not_returned_either2(i32* readonly %b, i32* readonly returned %r)
; CHECK: define i32* @not_captured_by_readonly_call_not_returned_either3(i32* readonly %b, i32* readonly returned %r)
; CHECK: define i32* @not_captured_by_readonly_call_not_returned_either2(i32* nocapture readonly %b, i32* readonly returned %r)
; CHECK: define i32* @not_captured_by_readonly_call_not_returned_either3(i32* nocapture readonly %b, i32* readonly returned %r)
;
; FIXME: The "nounwind" information is not derived to the fullest extend causing us to miss "nocapture" on %b in the following:
; CHECK: define i32* @not_captured_by_readonly_call_not_returned_either4(i32* readonly %b, i32* readonly returned %r)
define i32* @not_captured_by_readonly_call_not_returned_either1(i32* %b, i32* returned %r) #0 {
; CHECK: define i32* @not_captured_by_readonly_call_not_returned_either4(i32* nocapture readonly %b, i32* readonly returned %r)
define i32* @not_captured_by_readonly_call_not_returned_either1(i32* %b, i32* returned %r) {
entry:
%call = call i32* @readonly_unknown(i32* %b, i32* %r) nounwind
ret i32* %call
}
declare i32* @readonly_unknown_r1a(i32*, i32* returned) readonly
define i32* @not_captured_by_readonly_call_not_returned_either2(i32* %b, i32* %r) #0 {
define i32* @not_captured_by_readonly_call_not_returned_either2(i32* %b, i32* %r) {
entry:
%call = call i32* @readonly_unknown_r1a(i32* %b, i32* %r) nounwind
ret i32* %call
}
declare i32* @readonly_unknown_r1b(i32*, i32* returned) readonly nounwind
define i32* @not_captured_by_readonly_call_not_returned_either3(i32* %b, i32* %r) #0 {
define i32* @not_captured_by_readonly_call_not_returned_either3(i32* %b, i32* %r) {
entry:
%call = call i32* @readonly_unknown_r1b(i32* %b, i32* %r)
ret i32* %call
}
define i32* @not_captured_by_readonly_call_not_returned_either4(i32* %b, i32* %r) #0 {
define i32* @not_captured_by_readonly_call_not_returned_either4(i32* %b, i32* %r) nounwind {
entry:
%call = call i32* @readonly_unknown_r1a(i32* %b, i32* %r)
ret i32* %call

2
llvm/test/Transforms/FunctionAttrs/arg_returned.ll
View File

@ -1,5 +1,5 @@
; RUN: opt -functionattrs -S < %s | FileCheck %s --check-prefix=FNATTR
; RUN: opt -attributor -attributor-manifest-internal -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=6 -S < %s | FileCheck %s --check-prefix=ATTRIBUTOR
; RUN: opt -attributor -attributor-manifest-internal -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=7 -S < %s | FileCheck %s --check-prefix=ATTRIBUTOR
; RUN: opt -attributor -attributor-manifest-internal -attributor-disable=false -functionattrs -S < %s | FileCheck %s --check-prefix=BOTH
;
; Test cases specifically designed for the "returned" argument attribute.

29
llvm/test/Transforms/FunctionAttrs/nocapture.ll
View File

@ -39,6 +39,20 @@ l1:
ret i1 1 ; escaping value not caught by def-use chaining.
}
; c4b is c4 but without the escaping part
; FNATTR: define i1 @c4b(i32* %q, i32 %bitno)
; ATTRIBUTOR: define i1 @c4b(i32* nocapture readnone %q, i32 %bitno)
define i1 @c4b(i32* %q, i32 %bitno) {
%tmp = ptrtoint i32* %q to i32
%tmp2 = lshr i32 %tmp, %bitno
%bit = trunc i32 %tmp2 to i1
br i1 %bit, label %l1, label %l0
l0:
ret i1 0 ; not escaping!
l1:
ret i1 0 ; not escaping!
}
@lookup_table = global [2 x i1] [ i1 0, i1 1 ]
; FNATTR: define i1 @c5(i32* %q, i32 %bitno)
@ -331,5 +345,20 @@ entry:
ret void
}
declare i8* @unknownpi8pi8(i8*,i8* returned)
define i8* @test_returned1(i8* %A, i8* returned %B) nounwind readonly {
; ATTRIBUTOR: define i8* @test_returned1(i8* nocapture readonly %A, i8* readonly returned %B)
entry:
%p = call i8* @unknownpi8pi8(i8* %A, i8* %B)
ret i8* %p
}
define i8* @test_returned2(i8* %A, i8* %B) {
; ATTRIBUTOR: define i8* @test_returned2(i8* nocapture readonly %A, i8* readonly returned %B)
entry:
%p = call i8* @unknownpi8pi8(i8* %A, i8* %B) nounwind readonly
ret i8* %p
}
declare i8* @llvm.launder.invariant.group.p0i8(i8*)
declare i8* @llvm.strip.invariant.group.p0i8(i8*)

2
llvm/test/Transforms/FunctionAttrs/nonnull.ll
View File

@ -220,7 +220,7 @@ bb:
define dso_local noalias i32* @f3(i32* %arg) {
; FIXME: missing nonnull. It should be nonnull @f3(i32* nonnull readonly %arg)
; ATTRIBUTOR: define dso_local noalias i32* @f3(i32* readonly %arg)
; ATTRIBUTOR: define dso_local noalias i32* @f3(i32* nocapture readonly %arg)
bb:
; FIXME: missing nonnull. It should be @f1(i32* nonnull readonly %arg)
; ATTRIBUTOR: %tmp = call i32* @f1(i32* readonly %arg)

2
llvm/test/Transforms/FunctionAttrs/read_write_returned_arguments_scc.ll
View File

@ -1,4 +1,4 @@
; RUN: opt -functionattrs -enable-nonnull-arg-prop -attributor -attributor-manifest-internal -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=7 -S < %s | FileCheck %s
; RUN: opt -functionattrs -enable-nonnull-arg-prop -attributor -attributor-manifest-internal -attributor-disable=false -attributor-max-iterations-verify -attributor-max-iterations=8 -S < %s | FileCheck %s
;
; This is an evolved example to stress test SCC parameter attribute propagation.
; The SCC in this test is made up of the following six function, three of which