From 0437bfcc8338ec79f1d209daf975b9555e51e4b1 Mon Sep 17 00:00:00 2001
From: Johannes Doerfert <johannes@jdoerfert.de>
Date: Thu, 31 Oct 2019 20:03:13 -0500
Subject: [PATCH] [Attributor][FIX] NoCapture is not a subsuming property

We cannot look at the subsuming positions and take their nocapture bit
as shown with the two tests for which we derived nocapture on the call
site argument and readonly on the argument of the second before.
---
 llvm/lib/Transforms/IPO/Attributor.cpp        | 17 +++++++---
 .../Transforms/FunctionAttrs/arg_nocapture.ll | 31 +++++++++++++++++++
 2 files changed, 43 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
index a0677c194f17..6f0a4a858902 100644
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -3131,7 +3131,16 @@ struct AANoCaptureImpl : public AANoCapture {
 
   /// See AbstractAttribute::initialize(...).
   void initialize(Attributor &A) override {
-    AANoCapture::initialize(A);
+    if (hasAttr(getAttrKind(), /* IgnoreSubsumingPositions */ true)) {
+      indicateOptimisticFixpoint();
+      return;
+    }
+    Function *AnchorScope = getAnchorScope();
+    if (isFnInterfaceKind() &&
+        (!AnchorScope || !AnchorScope->hasExactDefinition())) {
+      indicatePessimisticFixpoint();
+      return;
+    }
 
     // You cannot "capture" null in the default address space.
     if (isa<ConstantPointerNull>(getAssociatedValue()) &&
@@ -3140,13 +3149,11 @@ struct AANoCaptureImpl : public AANoCapture {
       return;
     }
 
-    const IRPosition &IRP = getIRPosition();
-    const Function *F =
-        getArgNo() >= 0 ? IRP.getAssociatedFunction() : IRP.getAnchorScope();
+    const Function *F = getArgNo() >= 0 ? getAssociatedFunction() : AnchorScope;
 
     // Check what state the associated function can actually capture.
     if (F)
-      determineFunctionCaptureCapabilities(IRP, *F, *this);
+      determineFunctionCaptureCapabilities(getIRPosition(), *F, *this);
     else
       indicatePessimisticFixpoint();
   }
diff --git a/llvm/test/Transforms/FunctionAttrs/arg_nocapture.ll b/llvm/test/Transforms/FunctionAttrs/arg_nocapture.ll
index 18a4f7671472..ec7db076b36f 100644
--- a/llvm/test/Transforms/FunctionAttrs/arg_nocapture.ll
+++ b/llvm/test/Transforms/FunctionAttrs/arg_nocapture.ll
@@ -437,4 +437,35 @@ entry:
   ret i32* %call
 }
 
+
+declare i32* @unknown_i32p(i32*)
+define void @nocapture_is_not_subsumed_1(i32* nocapture %b) {
+; CHECK-LABEL: define {{[^@]+}}@nocapture_is_not_subsumed_1
+; CHECK-SAME: (i32* nocapture [[B:%.*]])
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CALL:%.*]] = call i32* @unknown_i32p(i32* [[B:%.*]])
+; CHECK-NEXT:    store i32 0, i32* [[CALL]]
+; CHECK-NEXT:    ret void
+;
+entry:
+  %call = call i32* @unknown_i32p(i32* %b)
+  store i32 0, i32* %call
+  ret void
+}
+
+declare i32* @readonly_i32p(i32*) readonly
+define void @nocapture_is_not_subsumed_2(i32* nocapture %b) {
+; CHECK-LABEL: define {{[^@]+}}@nocapture_is_not_subsumed_2
+; CHECK-SAME: (i32* nocapture [[B:%.*]])
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CALL:%.*]] = call i32* @readonly_i32p(i32* readonly [[B:%.*]])
+; CHECK-NEXT:    store i32 0, i32* [[CALL]]
+; CHECK-NEXT:    ret void
+;
+entry:
+  %call = call i32* @readonly_i32p(i32* %b)
+  store i32 0, i32* %call
+  ret void
+}
+
 attributes #0 = { noinline nounwind uwtable }