[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@269007 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 14d92d633b9ccbeccba75be84e29b0508bcaca48..0b5c85813b45cc93fe1f5f0394005c0f5433e3de 100644 (file)
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -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);
 }

diff --git a/test/Analysis/BasicAA/guards.ll b/test/Analysis/BasicAA/guards.ll
new file mode 100644 (file)
index 0000000..66cfb15
--- /dev/null
+++ b/test/Analysis/BasicAA/guards.ll
@@ -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"() ]
+}