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llvm-mirror/test/Analysis/GlobalsModRef/memset-escape.ll
James Molloy 07acfd5604 [GlobalsAA] Teach GlobalsAA about nocapture
Arguments to function calls marked "nocapture" can be marked as
non-escaping. However, nocapture is defined in terms of the lifetime
of the callee, and if the callee can directly or indirectly recurse to
the caller, the semantics of nocapture are invalid.

Therefore, we eagerly discover which SCC each function belongs to,
and later can check if callee and caller of a callsite belong to
the same SCC, in which case there could be recursion.

This means that we can't be so optimistic in
getModRefInfo(ImmutableCallsite) - previously we assumed all call
arguments never aliased with an escaping global. Now we need to check,
because a global could now be passed as an argument but still not
escape.

This also solves a related conformance problem: MemCpyOptimizer can
turn non-escaping stores of globals into calls to intrinsics like
llvm.memcpy/llvm/memset. This confuses GlobalsAA, which knows the
global can't escape and so returns NoModRef when queried, when
obviously a memcpy/memset call does indeed reference and modify its
arguments.

This fixes PR24800, PR24801, and PR24802.

llvm-svn: 248576
2015-09-25 15:39:29 +00:00

66 lines
2.2 KiB
LLVM

; RUN: opt < %s -O1 -S -enable-non-lto-gmr=true | 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 [3 x i32] zeroinitializer, align 4
@b = common global i32 0, align 4
; The important thing we're checking for here is the reload of (some element of)
; @a after the memset.
; CHECK-LABEL: @main
; CHECK: call void @llvm.memset.p0i8.i64{{.*}} @a
; CHECK: store i32 3
; CHECK: load i32, i32* getelementptr {{.*}} @a
; CHECK: icmp eq i32
; CHECK: br i1
define i32 @main() {
entry:
%retval = alloca i32, align 4
%c = alloca [1 x i32], align 4
store i32 0, i32* %retval, align 4
%0 = bitcast [1 x i32]* %c to i8*
call void @llvm.memset.p0i8.i64(i8* %0, i8 0, i64 4, i32 4, i1 false)
store i32 1, i32* getelementptr inbounds ([3 x i32], [3 x i32]* @a, i64 0, i64 2), align 4
store i32 0, i32* @b, align 4
br label %for.cond
for.cond: ; preds = %for.inc, %entry
%1 = load i32, i32* @b, align 4
%cmp = icmp slt i32 %1, 3
br i1 %cmp, label %for.body, label %for.end
for.body: ; preds = %for.cond
%2 = load i32, i32* @b, align 4
%idxprom = sext i32 %2 to i64
%arrayidx = getelementptr inbounds [3 x i32], [3 x i32]* @a, i64 0, i64 %idxprom
store i32 0, i32* %arrayidx, align 4
br label %for.inc
for.inc: ; preds = %for.body
%3 = load i32, i32* @b, align 4
%inc = add nsw i32 %3, 1
store i32 %inc, i32* @b, align 4
br label %for.cond
for.end: ; preds = %for.cond
%4 = load i32, i32* getelementptr inbounds ([3 x i32], [3 x i32]* @a, i64 0, i64 2), align 4
%cmp1 = icmp ne i32 %4, 0
br i1 %cmp1, label %if.then, label %if.end
if.then: ; preds = %for.end
call void @abort() #3
unreachable
if.end: ; preds = %for.end
ret i32 0
}
; Function Attrs: nounwind argmemonly
declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) nounwind argmemonly
; Function Attrs: noreturn nounwind
declare void @abort() noreturn nounwind