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[StackSafety] Skip ambiguous lifetime analysis

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If we can't identify alloca used in lifetime marker we
need to assume to worst case scenario.

Reviewed By: eugenis

Differential Revision: https://reviews.llvm.org/D84630
This commit is contained in:
Vitaly Buka 2020-08-06 19:10:02 -07:00
parent 567e88646c
commit 3b944733de
4 changed files with 93 additions and 37 deletions
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2
include/llvm/Analysis/StackLifetime.h
View File

@ -121,6 +121,8 @@ private:
DenseMap<const BasicBlock *, SmallVector<std::pair<unsigned, Marker>, 4>>
BBMarkers;
bool HasUnknownLifetimeStartOrEnd = false;
void dumpAllocas() const;
void dumpBlockLiveness() const;
void dumpLiveRanges() const;

58
lib/Analysis/StackLifetime.cpp
View File

@ -11,6 +11,7 @@
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/AssemblyAnnotationWriter.h"
#include "llvm/IR/BasicBlock.h"
@ -63,42 +64,27 @@ bool StackLifetime::isAliveAfter(const AllocaInst *AI,
return getLiveRange(AI).test(InstNum);
}
static bool readMarker(const Instruction *I, bool *IsStart) {
if (!I->isLifetimeStartOrEnd())
return false;
auto *II = cast<IntrinsicInst>(I);
*IsStart = II->getIntrinsicID() == Intrinsic::lifetime_start;
return true;
}
void StackLifetime::collectMarkers() {
InterestingAllocas.resize(NumAllocas);
DenseMap<const BasicBlock *, SmallDenseMap<const IntrinsicInst *, Marker>>
BBMarkerSet;
// Compute the set of start/end markers per basic block.
for (unsigned AllocaNo = 0; AllocaNo < NumAllocas; ++AllocaNo) {
const AllocaInst *AI = Allocas[AllocaNo];
SmallVector<const Instruction *, 8> WorkList;
WorkList.push_back(AI);
while (!WorkList.empty()) {
const Instruction *I = WorkList.pop_back_val();
for (const User *U : I->users()) {
if (auto *BI = dyn_cast<BitCastInst>(U)) {
WorkList.push_back(BI);
continue;
}
auto *UI = dyn_cast<IntrinsicInst>(U);
if (!UI)
continue;
bool IsStart;
if (!readMarker(UI, &IsStart))
continue;
if (IsStart)
InterestingAllocas.set(AllocaNo);
BBMarkerSet[UI->getParent()][UI] = {AllocaNo, IsStart};
for (const BasicBlock *BB : depth_first(&F)) {
for (const Instruction &I : *BB) {
const IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I);
if (!II || !II->isLifetimeStartOrEnd())
continue;
const AllocaInst *AI = llvm::findAllocaForValue(II->getArgOperand(1));
if (!AI) {
HasUnknownLifetimeStartOrEnd = true;
continue;
}
bool IsStart = II->getIntrinsicID() == Intrinsic::lifetime_start;
unsigned AllocaNo = AllocaNumbering[AI];
if (IsStart)
InterestingAllocas.set(AllocaNo);
BBMarkerSet[BB][II] = {AllocaNo, IsStart};
}
}
@ -304,6 +290,20 @@ StackLifetime::StackLifetime(const Function &F,
}
void StackLifetime::run() {
if (HasUnknownLifetimeStartOrEnd) {
// There is marker which we can't assign to a specific alloca, so we
// fallback to the most conservative results for the type.
switch (Type) {
case LivenessType::May:
LiveRanges.resize(NumAllocas, getFullLiveRange());
break;
case LivenessType::Must:
LiveRanges.resize(NumAllocas, LiveRange(Instructions.size()));
break;
}
return;
}
LiveRanges.resize(NumAllocas, LiveRange(Instructions.size()));
for (unsigned I = 0; I < NumAllocas; ++I)
if (!InterestingAllocas.test(I))

59
test/Analysis/StackSafetyAnalysis/lifetime.ll
View File

@ -742,7 +742,7 @@ if.end:
; MAY-NEXT: Alive: <x y>
; MUST-NEXT: Alive: <y>
ret void
ret void
}
define void @unreachable() {
@ -778,7 +778,62 @@ end:
; CHECK: end:
; CHECK-NEXT: Alive: <x y>
ret void
ret void
}
define void @non_alloca(i8* %p) {
; CHECK-LABEL: define void @non_alloca
entry:
; CHECK: entry:
; MAY-NEXT: Alive: <x y>
; MUST-NEXT: Alive: <>
%x = alloca i8, align 4
%y = alloca i8, align 4
call void @llvm.lifetime.start.p0i8(i64 4, i8* %p)
; CHECK: call void @llvm.lifetime.start.p0i8(i64 4, i8* %p)
; MAY-NEXT: Alive: <x y>
; MUST-NEXT: Alive: <>
call void @llvm.lifetime.start.p0i8(i64 4, i8* %x)
; CHECK: call void @llvm.lifetime.start.p0i8(i64 4, i8* %x)
; MAY-NEXT: Alive: <x y>
; MUST-NEXT: Alive: <>
call void @llvm.lifetime.end.p0i8(i64 4, i8* %p)
; CHECK: call void @llvm.lifetime.end.p0i8(i64 4, i8* %p)
; MAY-NEXT: Alive: <x y>
; MUST-NEXT: Alive: <>
ret void
}
define void @select_alloca(i1 %v) {
; CHECK-LABEL: define void @select_alloca
entry:
; CHECK: entry:
; MAY-NEXT: Alive: <x y>
; MUST-NEXT: Alive: <>
%x = alloca i8, align 4
%y = alloca i8, align 4
%cxcy = select i1 %v, i8* %x, i8* %y
call void @llvm.lifetime.start.p0i8(i64 1, i8* %cxcy)
; CHECK: call void @llvm.lifetime.start.p0i8(i64 1, i8* %cxcy)
; MAY-NEXT: Alive: <x y>
; MUST-NEXT: Alive: <>
call void @llvm.lifetime.start.p0i8(i64 1, i8* %x)
; CHECK: call void @llvm.lifetime.start.p0i8(i64 1, i8* %x)
; MAY-NEXT: Alive: <x y>
; MUST-NEXT: Alive: <>
call void @llvm.lifetime.end.p0i8(i64 1, i8* %x)
; CHECK: call void @llvm.lifetime.end.p0i8(i64 1, i8* %x)
; MAY-NEXT: Alive: <x y>
; MUST-NEXT: Alive: <>
ret void
}
declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture)

11
test/CodeGen/AArch64/stack-tagging.ll
View File

@ -192,10 +192,9 @@ another_bb:
; CHECK: alloca { i32, [12 x i8] }, align 16
; CHECK: call { i32, [12 x i8] }* @llvm.aarch64.tagp
; CHECK: call void @llvm.aarch64.settag(
; SSI: alloca i32, align 4
; NOSSI: alloca { i32, [12 x i8] }, align 16
; NOSSI: call { i32, [12 x i8] }* @llvm.aarch64.tagp
; NOSSI: call void @llvm.aarch64.settag(
; CHECK: alloca { i32, [12 x i8] }, align 16
; CHECK: call { i32, [12 x i8] }* @llvm.aarch64.tagp
; CHECK: call void @llvm.aarch64.settag(
; CHECK: store i32
; CHECK: call void @noUse32(i32*
; CHECK: store i32
@ -203,7 +202,7 @@ another_bb:
; CHECK: call void @noUse32(i32*
; CHECK: call void @llvm.aarch64.settag(
; CHECK: call void @llvm.aarch64.settag(
; NOSSI: call void @llvm.aarch64.settag(
; CHECK: call void @llvm.aarch64.settag(
; CHECK: ret void
!0 = !{}
!0 = !{}