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Add regression test for r331976

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In general, it's difficult to poke the ConstantExpr code in CFLAA, since
LLVM is so great at eagerly reducing ConstantExprs. :)

Sadly, this only shows a functional difference from before the patch
because CFLAA has some special logic around taking loads of non-pointers
into account. Namely, with the broken select behavior, CFLAA will
completely fail to take note of @g3. Since CFLAA doesn't have any record
about @g3 when we do an alias query for @g3 and %a, it conservatively
answers MayAlias. When we properly take @g3 into account with the new
select logic, we get NoAlias for this query.

I suspect that the aforementioned "special logic" isn't completely
correct, but this test-case should prevent future wonky aliasing results
from appearing for these flavors of ConstantExprs, so I think it's still
worth having.

llvm-svn: 332017
This commit is contained in:
George Burgess IV 2018-05-10 18:37:54 +00:00
parent cc71215e80
commit cef84e7236
1 changed files with 30 additions and 0 deletions
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30
test/Analysis/CFLAliasAnalysis/Steensgaard/const-exprs.ll Normal file
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; RUN: opt %s -S -disable-basicaa -cfl-steens-aa -aa-eval -print-all-alias-modref-info 2>&1 | FileCheck %s
;
; Regression: we weren't properly checking constexpr selects.
@g = extern_weak dso_local global i32, align 4
@g2 = extern_weak dso_local global i32, align 4
@g3 = extern_weak dso_local global i32, align 4
; CHECK-LABEL: Function: foo
; CHECK: NoAlias: i32* select (i1 icmp ne (i32* @g, i32* null), i32* @g2, i32* @g3), i32** %a
; CHECK: NoAlias: i32* %b, i32** %a
; CHECK: MayAlias: i32* %b, i32* select (i1 icmp ne (i32* @g, i32* null), i32* @g2, i32* @g3)
; CHECK: NoAlias: i32* @g2, i32** %a
; CHECK: MayAlias: i32* @g2, i32* select (i1 icmp ne (i32* @g, i32* null), i32* @g2, i32* @g3)
; CHECK: MayAlias: i32* %b, i32* @g2
; CHECK: NoAlias: i32* @g3, i32** %a
; CHECK: MayAlias: i32* @g3, i32* select (i1 icmp ne (i32* @g, i32* null), i32* @g2, i32* @g3)
; CHECK: MayAlias: i32* %b, i32* @g3
; CHECK: MayAlias: i32* @g2, i32* @g3
define void @foo() {
entry:
%a = alloca i32*, align 8
store i32* select (i1 icmp ne (i32* @g, i32* null), i32* @g2, i32* @g3), i32** %a
%b = load i32*, i32** %a
%c = load i32, i32* %b
%d = load i32, i32* @g2
%e = load i32, i32* @g3
ret void
}