[BasicAA] Improve precision of alloca vs. inbounds GEP alias queries
If a we have (a) a GEP and (b) a pointer based on an alloca, and the
beginning of the object the GEP points would have a negative offset with
repsect to the alloca, then the GEP can not alias pointer (b).
For example, consider code like:
struct { int f0, int f1, ...} foo;
...
foo alloca;
foo *random = bar(alloca);
int *f0 = &alloca.f0
int *f1 = &random->f1;
Which is lowered, approximately, to:
%alloca = alloca %struct.foo
%random = call %struct.foo* @random(%struct.foo* %alloca)
%f0 = getelementptr inbounds %struct, %struct.foo* %alloca, i32 0, i32 0
%f1 = getelementptr inbounds %struct, %struct.foo* %random, i32 0, i32 1
Assume %f1 and %f0 alias. Then %f1 would point into the object allocated
by %alloca. Since the %f1 GEP is inbounds, that means %random must also
point into the same object. But since %f0 points to the beginning of %alloca,
the highest %f1 can be is (%alloca + 3). This means %random can not be higher
than (%alloca - 1), and so is not inbounds, a contradiction.
Differential Revision: http://reviews.llvm.org/D20495
llvm-svn: 270777
2016-05-26 06:23:08 +08:00
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; RUN: opt < %s -basicaa -aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
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target datalayout = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128"
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target triple = "i386-unknown-linux-gnu"
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declare i32* @random.i32(i32* %ptr)
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; CHECK-LABEL: Function: arr:
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; CHECK-DAG: MayAlias: i32* %alloca, i32* %p0
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; CHECK-DAG: NoAlias: i32* %alloca, i32* %p1
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define void @arr() {
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%alloca = alloca i32, i32 4
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%random = call i32* @random.i32(i32* %alloca)
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%p0 = getelementptr inbounds i32, i32* %random, i32 0
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%p1 = getelementptr inbounds i32, i32* %random, i32 1
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ret void
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}
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; CHECK-LABEL: Function: arg:
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; CHECK-DAG: MayAlias: i32* %arg, i32* %p0
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; CHECK-DAG: MayAlias: i32* %arg, i32* %p1
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define void @arg(i32* %arg) {
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%random = call i32* @random.i32(i32* %arg)
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%p0 = getelementptr inbounds i32, i32* %random, i32 0
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%p1 = getelementptr inbounds i32, i32* %random, i32 1
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ret void
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}
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2016-05-27 03:30:49 +08:00
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@gv = global i32 1
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; CHECK-LABEL: Function: global:
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; CHECK-DAG: MayAlias: i32* %p0, i32* @gv
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; CHECK-DAG: NoAlias: i32* %p1, i32* @gv
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define void @global() {
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%random = call i32* @random.i32(i32* @gv)
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%p0 = getelementptr inbounds i32, i32* %random, i32 0
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%p1 = getelementptr inbounds i32, i32* %random, i32 1
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ret void
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}
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[BasicAA] Improve precision of alloca vs. inbounds GEP alias queries
If a we have (a) a GEP and (b) a pointer based on an alloca, and the
beginning of the object the GEP points would have a negative offset with
repsect to the alloca, then the GEP can not alias pointer (b).
For example, consider code like:
struct { int f0, int f1, ...} foo;
...
foo alloca;
foo *random = bar(alloca);
int *f0 = &alloca.f0
int *f1 = &random->f1;
Which is lowered, approximately, to:
%alloca = alloca %struct.foo
%random = call %struct.foo* @random(%struct.foo* %alloca)
%f0 = getelementptr inbounds %struct, %struct.foo* %alloca, i32 0, i32 0
%f1 = getelementptr inbounds %struct, %struct.foo* %random, i32 0, i32 1
Assume %f1 and %f0 alias. Then %f1 would point into the object allocated
by %alloca. Since the %f1 GEP is inbounds, that means %random must also
point into the same object. But since %f0 points to the beginning of %alloca,
the highest %f1 can be is (%alloca + 3). This means %random can not be higher
than (%alloca - 1), and so is not inbounds, a contradiction.
Differential Revision: http://reviews.llvm.org/D20495
llvm-svn: 270777
2016-05-26 06:23:08 +08:00
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; CHECK-LABEL: Function: struct:
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; CHECK-DAG: MayAlias: i32* %f0, i32* %p0
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; CHECK-DAG: MayAlias: i32* %f1, i32* %p0
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; CHECK-DAG: NoAlias: i32* %f0, i32* %p1
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; CHECK-DAG: MayAlias: i32* %f1, i32* %p1
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%struct = type { i32, i32, i32 }
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define void @struct() {
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%alloca = alloca %struct
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%alloca.i32 = bitcast %struct* %alloca to i32*
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%random = call i32* @random.i32(i32* %alloca.i32)
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%f0 = getelementptr inbounds %struct, %struct* %alloca, i32 0, i32 0
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%f1 = getelementptr inbounds %struct, %struct* %alloca, i32 0, i32 1
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%p0 = getelementptr inbounds i32, i32* %random, i32 0
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%p1 = getelementptr inbounds i32, i32* %random, i32 1
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ret void
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}
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; CHECK-LABEL: Function: complex1:
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; CHECK-DAG: MayAlias: i32* %a2.0, i32* %r2.0
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; CHECK-DAG: NoAlias: i32* %a2.0, i32* %r2.1
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; CHECK-DAG: MayAlias: i32* %a2.0, i32* %r2.i
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; CHECK-DAG: MayAlias: i32* %a2.0, i32* %r2.1i
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; CHECK-DAG: NoAlias: i32* %a1, i32* %r2.0
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; CHECK-DAG: NoAlias: i32* %a1, i32* %r2.1
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; CHECK-DAG: NoAlias: i32* %a1, i32* %r2.i
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; CHECK-DAG: NoAlias: i32* %a1, i32* %r2.1i
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%complex = type { i32, i32, [4 x i32] }
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define void @complex1(i32 %i) {
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%alloca = alloca %complex
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%alloca.i32 = bitcast %complex* %alloca to i32*
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%r.i32 = call i32* @random.i32(i32* %alloca.i32)
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%random = bitcast i32* %r.i32 to %complex*
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%a1 = getelementptr inbounds %complex, %complex* %alloca, i32 0, i32 1
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%a2.0 = getelementptr inbounds %complex, %complex* %alloca, i32 0, i32 2, i32 0
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%r2.0 = getelementptr inbounds %complex, %complex* %random, i32 0, i32 2, i32 0
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%r2.1 = getelementptr inbounds %complex, %complex* %random, i32 0, i32 2, i32 1
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%r2.i = getelementptr inbounds %complex, %complex* %random, i32 0, i32 2, i32 %i
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%r2.1i = getelementptr inbounds i32, i32* %r2.1, i32 %i
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ret void
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}
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; CHECK-LABEL: Function: complex2:
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; CHECK-DAG: NoAlias: i32* %alloca, i32* %p120
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; CHECK-DAG: NoAlias: i32* %alloca, i32* %pi20
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; CHECK-DAG: NoAlias: i32* %alloca, i32* %pij1
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; CHECK-DAG: MayAlias: i32* %a3, i32* %pij1
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%inner = type { i32, i32 }
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%outer = type { i32, i32, [10 x %inner] }
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declare %outer* @rand_outer(i32* %p)
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define void @complex2(i32 %i, i32 %j) {
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%alloca = alloca i32, i32 128
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%a3 = getelementptr inbounds i32, i32* %alloca, i32 3
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%random = call %outer* @rand_outer(i32* %alloca)
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%p120 = getelementptr inbounds %outer, %outer* %random, i32 1, i32 2, i32 2, i32 0
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%pi20 = getelementptr inbounds %outer, %outer* %random, i32 %i, i32 2, i32 2, i32 0
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%pij1 = getelementptr inbounds %outer, %outer* %random, i32 %i, i32 2, i32 %j, i32 1
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ret void
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}
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