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[BasicAA] Guard intrinsics don't write to memory 

Summary:
The idea is very close to what we do for assume intrinsics: we mark the
guard intrinsics as writing to arbitrary memory to maintain control
dependence, but under the covers we teach AA that they do not mod any
particular memory location.

Reviewers: chandlerc, hfinkel, gbiv, reames

Subscribers: george.burgess.iv, mcrosier, llvm-commits

Differential Revision: http://reviews.llvm.org/D19575

llvm-svn: 269007
This commit is contained in:
Sanjoy Das 2016-05-10 02:35:41 +00:00
parent a00b97f780
commit d47f42435a
2 changed files with 62 additions and 4 deletions
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36
llvm/lib/Analysis/BasicAliasAnalysis.cpp
View File

@ -649,9 +649,9 @@ ModRefInfo BasicAAResult::getArgModRefInfo(ImmutableCallSite CS,
return AAResultBase::getArgModRefInfo(CS, ArgIdx);
}
static bool isAssumeIntrinsic(ImmutableCallSite CS) {
static bool isIntrinsicCall(ImmutableCallSite CS, Intrinsic::ID IID) {
const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
return II && II->getIntrinsicID() == Intrinsic::assume;
return II && II->getIntrinsicID() == IID;
}
#ifndef NDEBUG
@ -769,9 +769,19 @@ ModRefInfo BasicAAResult::getModRefInfo(ImmutableCallSite CS,
// While the assume intrinsic is marked as arbitrarily writing so that
// proper control dependencies will be maintained, it never aliases any
// particular memory location.
if (isAssumeIntrinsic(CS))
if (isIntrinsicCall(CS, Intrinsic::assume))
return MRI_NoModRef;
// Like assumes, guard intrinsics are also marked as arbitrarily writing so
// that proper control dependencies are maintained but they never mods any
// particular memory location.
//
// *Unlike* assumes, guard intrinsics are modeled as reading memory since the
// heap state at the point the guard is issued needs to be consistent in case
// the guard invokes the "deopt" continuation.
if (isIntrinsicCall(CS, Intrinsic::experimental_guard))
return MRI_Ref;
// The AAResultBase base class has some smarts, lets use them.
return AAResultBase::getModRefInfo(CS, Loc);
}
@ -781,9 +791,27 @@ ModRefInfo BasicAAResult::getModRefInfo(ImmutableCallSite CS1,
// While the assume intrinsic is marked as arbitrarily writing so that
// proper control dependencies will be maintained, it never aliases any
// particular memory location.
if (isAssumeIntrinsic(CS1) || isAssumeIntrinsic(CS2))
if (isIntrinsicCall(CS1, Intrinsic::assume) ||
isIntrinsicCall(CS2, Intrinsic::assume))
return MRI_NoModRef;
// Like assumes, guard intrinsics are also marked as arbitrarily writing so
// that proper control dependencies are maintained but they never mod any
// particular memory location.
//
// *Unlike* assumes, guard intrinsics are modeled as reading memory since the
// heap state at the point the guard is issued needs to be consistent in case
// the guard invokes the "deopt" continuation.
// NB! This function is *not* commutative, so we specical case two
// possibilities for guard intrinsics.
if (isIntrinsicCall(CS1, Intrinsic::experimental_guard))
return getModRefBehavior(CS2) & MRI_Mod ? MRI_Ref : MRI_NoModRef;
if (isIntrinsicCall(CS2, Intrinsic::experimental_guard))
return getModRefBehavior(CS1) & MRI_Mod ? MRI_Mod : MRI_NoModRef;
// The AAResultBase base class has some smarts, lets use them.
return AAResultBase::getModRefInfo(CS1, CS2);
}

30
llvm/test/Analysis/BasicAA/guards.ll Normal file
View File

@ -0,0 +1,30 @@
; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
target datalayout = "e-p:32:32:32-i1:8:32-i8:8:32-i16:16:32-i32:32:32-i64:32:32-f32:32:32-f64:32:32-v64:32:64-v128:32:128-a0:0:32-n32"
declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, i64, i32, i1) #0
declare void @llvm.experimental.guard(i1, ...)
declare void @unknown_but_readonly() readonly
define void @test1(i8* %P, i8* %Q) {
tail call void(i1,...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i32 1, i1 false)
ret void
; CHECK-LABEL: Function: test1:
; CHECK: Just Ref: Ptr: i8* %P <-> tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
; CHECK: Just Ref: Ptr: i8* %Q <-> tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
; CHECK: Both ModRef: Ptr: i8* %P <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i32 1, i1 false)
; CHECK: Both ModRef: Ptr: i8* %Q <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i32 1, i1 false)
; CHECK: Just Ref: tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ] <-> tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i32 1, i1 false)
; CHECK: Just Mod: tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i32 1, i1 false) <-> tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
}
define void @test2() {
tail call void(i1,...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
tail call void @unknown_but_readonly()
ret void
; CHECK-LABEL: Function: test2:
; CHECK: NoModRef: tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ] <-> tail call void @unknown_but_readonly()
; CHECK: NoModRef: tail call void @unknown_but_readonly() <-> tail call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
}