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[DSE] Enable removal of lifetime intrinsics in terminating blocks

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Usually DSE is not supposed to remove lifetime intrinsics, but it's
actually ok to remove them for dead objects in terminating blocks,
because they convey no extra information there. Until we hit a lifetime
start that cannot be removed, that is. Because from that point on the
lifetime intrinsics become interesting again, e.g. for stack coloring.

Reviewers: reames

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D11710

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@245542 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bjorn Steinbrink 2015-08-20 08:25:28 +00:00
parent cce9e53d02
commit 1ca4f6f1ca
2 changed files with 81 additions and 5 deletions
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33
lib/Transforms/Scalar/DeadStoreElimination.cpp
View File

@ -788,15 +788,33 @@ bool DSE::handleEndBlock(BasicBlock &BB) {
const DataLayout &DL = BB.getModule()->getDataLayout();
// becomes false once lifetime intrinsics are observable or useful for stack
// coloring
bool canRemoveLifetimeIntrinsics = true;
// Scan the basic block backwards
for (BasicBlock::iterator BBI = BB.end(); BBI != BB.begin(); ){
--BBI;
// If we find a store, check to see if it points into a dead stack value.
if (hasMemoryWrite(BBI, *TLI) && isRemovable(BBI)) {
Value *V = nullptr;
if (canRemoveLifetimeIntrinsics)
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(BBI))
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::lifetime_start:
case Intrinsic::lifetime_end:
V = II->getArgOperand(1);
break;
}
if (!V && hasMemoryWrite(BBI, *TLI) && isRemovable(BBI))
V = getStoredPointerOperand(BBI);
// If we found a store, check to see if it points into a dead stack value.
if (V) {
// See through pointer-to-pointer bitcasts
SmallVector<Value *, 4> Pointers;
GetUnderlyingObjects(getStoredPointerOperand(BBI), Pointers, DL);
GetUnderlyingObjects(V, Pointers, DL);
// Stores to stack values are valid candidates for removal.
bool AllDead = true;
@ -844,6 +862,15 @@ bool DSE::handleEndBlock(BasicBlock &BB) {
continue;
}
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(BBI))
if (II->getIntrinsicID() == Intrinsic::lifetime_start) {
// We found a lifetime start for a live object, which we could not
// remove. So we must stop removing lifetime intrinsics from this block
// because they're useful for stack coloring again
canRemoveLifetimeIntrinsics = false;
continue;
}
if (auto CS = CallSite(BBI)) {
// Remove allocation function calls from the list of dead stack objects;
// there can't be any references before the definition.

53
test/Transforms/DeadStoreElimination/lifetime.ll
View File

@ -5,14 +5,16 @@ target datalayout = "E-p:64:64:64-a0:0:8-f32:32:32-f64:64:64-i1:8:8-i8:8:8-i16:1
declare void @llvm.lifetime.start(i64, i8* nocapture) nounwind
declare void @llvm.lifetime.end(i64, i8* nocapture) nounwind
declare void @llvm.memset.p0i8.i8(i8* nocapture, i8, i8, i32, i1) nounwind
declare void @callee(i8*)
define void @test1() {
; CHECK-LABEL: @test1(
%A = alloca i8
store i8 0, i8* %A ;; Written to by memset
; CHECK-NOT: store
call void @llvm.lifetime.end(i64 1, i8* %A)
; CHECK: lifetime.end
; CHECK-NOT: lifetime.end
call void @llvm.memset.p0i8.i8(i8* %A, i8 0, i8 -1, i32 0, i1 false)
; CHECK-NOT: memset
@ -22,7 +24,7 @@ define void @test1() {
}
define void @test2(i32* %P) {
; CHECK: test2
; CHECK-LABEL: test2
%Q = getelementptr i32, i32* %P, i32 1
%R = bitcast i32* %Q to i8*
call void @llvm.lifetime.start(i64 4, i8* %R)
@ -34,4 +36,51 @@ define void @test2(i32* %P) {
ret void
}
define void @test3(i8*) {
; CHECK-LABEL: test3
%a = alloca i8
call void @llvm.lifetime.start(i64 1, i8* %a)
; CHECK-NOT: lifetime.start
call void @llvm.lifetime.end(i64 1, i8* %a)
; CHECK-NOT: lifetime.end
call void @llvm.lifetime.start(i64 1, i8* undef)
; CHECK-NOT: lifetime.start
call void @llvm.lifetime.end(i64 1, i8* undef)
; CHECK-NOT: lifetime.end
ret void
}
define void @test4(i8*) {
; CHECK-LABEL: test4
%a = alloca i8
call void @llvm.lifetime.start(i64 1, i8* %a)
; CHECK: lifetime.start
call void @llvm.lifetime.end(i64 1, i8* %a)
; CHECK: lifetime.end
call void @llvm.lifetime.start(i64 1, i8* %0)
; CHECK: lifetime.start
call void @llvm.lifetime.end(i64 1, i8* %0)
; CHECK: lifetime.end
call void @llvm.lifetime.start(i64 1, i8* %a)
; CHECK-NOT: lifetime.start
call void @llvm.lifetime.end(i64 1, i8* %a)
; CHECK-NOT: lifetime.end
ret void
}
define void @test5() {
; CHECK-LABEL: test5
%a = alloca i8
%b = alloca i8
call void @llvm.lifetime.start(i64 1, i8* %a)
; CHECK: lifetime.start
call void @llvm.lifetime.end(i64 1, i8* %a)
; CHECK: lifetime.end
call void @llvm.lifetime.start(i64 1, i8* %b)
; CHECK: lifetime.start
call void @callee(i8* %b)
; CHECK: call void @callee
call void @llvm.lifetime.end(i64 1, i8* %b)
; CHECK-NOT: lifetime.end
ret void
}