From 9971a6841c2df37b57eadc27d7a7ad4440cd8b70 Mon Sep 17 00:00:00 2001
From: James Molloy <james.molloy@arm.com>
Date: Thu, 7 Jan 2016 13:33:28 +0000
Subject: [GlobalsAA] Partially back out r248576

See PR25822 for a more full summary, but we were conflating the concepts of "capture" and "escape". We were proving nocapture and using that proof to infer noescape, which is not true. Escaped-ness is a function-local property - as soon as a value is used in a call argument it escapes. Capturedness is a related but distinct property. It implies a *temporally limited* escape. Consider:

  static int a;
  int b;
  int g(int * nocapture arg);
  int f() {
    a = 2;  // Even though a escapes to g, it is not captured so can be treated as non-escaping here.
    g(&a);  // But here it must be treated as escaping.
    g(&b);  // Now that g(&a) has returned we know it was not captured so we can treat it as non-escaping again.
  }

The original commit did not sufficiently understand this nuance and so caused PR25822 and PR26046.

r248576 included both a performance improvement (which has been backed out) and a related conformance fix (which has been kept along with its testcase).

llvm-svn: 257058
---
 llvm/test/Analysis/GlobalsModRef/nocapture.ll | 57 ---------------------------
 1 file changed, 57 deletions(-)
 delete mode 100644 llvm/test/Analysis/GlobalsModRef/nocapture.ll

(limited to 'llvm/test')

diff --git a/llvm/test/Analysis/GlobalsModRef/nocapture.ll b/llvm/test/Analysis/GlobalsModRef/nocapture.ll
deleted file mode 100644
index 0cb80a10f8d..00000000000
--- a/llvm/test/Analysis/GlobalsModRef/nocapture.ll
+++ /dev/null
@@ -1,57 +0,0 @@
-; RUN: opt < %s -globals-aa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
-
-target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
-target triple = "x86_64-apple-macosx10.10.0"
-
-@a = internal global i32 0, align 4
-@b = internal global i32 0, align 4
-
-define void @g(i32* %p, void (i32*)* nocapture %ptr) {
-entry:
-  tail call void %ptr(i32* %p) #1
-  ret void
-}
-
-; CHECK-LABEL: Function: f
-; CHECK: MayAlias: i32* %p, i32* @a
-; CHECK: MayAlias: i32* %q, i32* @a
-define i32 @f(i32 %n, i32* nocapture readonly %p, i32* nocapture %q, void (i32*)* nocapture %ptr) {
-entry:
-  tail call void @g(i32* nonnull @a, void (i32*)* %ptr)
-  %arrayidx = getelementptr inbounds i32, i32* %p, i64 0
-  %z1 = load i32, i32* %arrayidx, align 4
-  %z2 = load i32, i32* %q, align 4
-  %add = add nsw i32 %z2, %z1
-  store i32 %add, i32* %q, align 4
-  ret i32 4
-}
-
-define void @g2(i32* nocapture %p, void (i32*)* nocapture %ptr) {
-entry:
-  tail call void %ptr(i32* %p) #1
-  ret void
-}
-
-; CHECK-LABEL: Function: f2
-; CHECK: NoAlias: i32* %p, i32* @b
-; CHECK: NoAlias: i32* %q, i32* @b
-define i32 @f2(i32 %n, i32* nocapture readonly %p, i32* nocapture %q, void (i32*)* nocapture %ptr) {
-entry:
-  tail call void @g2(i32* nonnull @b, void (i32*)* %ptr)
-  %arrayidx = getelementptr inbounds i32, i32* %p, i64 0
-  %z1 = load i32, i32* %arrayidx, align 4
-  %z2 = load i32, i32* %q, align 4
-  %add = add nsw i32 %z2, %z1
-  store i32 %add, i32* %q, align 4
-  ret i32 4
-}
-
-declare void @g3()
-
-; CHECK-LABEL: Function: f3
-; CHECK: NoAlias: i32* %p, i32* @b
-define void @f3(i32* nocapture readonly %p) {
-entry:
-  tail call void @g3() [ "deopt"(i32* @b, i32 *%p) ]
-  unreachable
-}
-- 
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