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[GlobalsModRef] Apply indirect-global rule to all globals initialized from noalias calls 

Extend the existing malloc-family specific optimization to all noalias calls.  This allows us to handle allocation wrappers, and removes a dependency on a lib-func check in favor of generic attribute usage.

Differential Revision: https://reviews.llvm.org/D116980
This commit is contained in:
Philip Reames 2022-01-11 08:40:03 -08:00
parent 20404d820c
commit e838949bee
2 changed files with 7 additions and 11 deletions
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8
llvm/lib/Analysis/GlobalsModRef.cpp
View File

@ -401,14 +401,14 @@ bool GlobalsAAResult::AnalyzeUsesOfPointer(Value *V,
/// AnalyzeIndirectGlobalMemory - We found an non-address-taken global variable
/// which holds a pointer type. See if the global always points to non-aliased
/// heap memory: that is, all initializers of the globals are allocations, and
/// those allocations have no use other than initialization of the global.
/// heap memory: that is, all initializers of the globals store a value known
/// to be obtained via a noalias return function call which have no other use.
/// Further, all loads out of GV must directly use the memory, not store the
/// pointer somewhere. If this is true, we consider the memory pointed to by
/// GV to be owned by GV and can disambiguate other pointers from it.
bool GlobalsAAResult::AnalyzeIndirectGlobalMemory(GlobalVariable *GV) {
// Keep track of values related to the allocation of the memory, f.e. the
// value produced by the malloc call and any casts.
// value produced by the noalias call and any casts.
std::vector<Value *> AllocRelatedValues;
// If the initializer is a valid pointer, bail.
@ -438,7 +438,7 @@ bool GlobalsAAResult::AnalyzeIndirectGlobalMemory(GlobalVariable *GV) {
// Check the value being stored.
Value *Ptr = getUnderlyingObject(SI->getOperand(0));
if (!isAllocLikeFn(Ptr, &GetTLI(*SI->getFunction())))
if (!isNoAliasCall(Ptr))
return false; // Too hard to analyze.
// Analyze all uses of the allocation. If any of them are used in a

10
llvm/test/Analysis/GlobalsModRef/indirect-global.ll
View File

@ -7,7 +7,7 @@
@G = internal global i32* null ; <i32**> [#uses=3]
declare i8* @malloc(i32)
declare noalias i8* @malloc(i32)
define void @malloc_init() {
; CHECK-LABEL: @malloc_init(
; CHECK-NEXT: [[A:%.*]] = call dereferenceable_or_null(4) i8* @malloc(i32 4)
@ -36,7 +36,7 @@ define i32 @malloc_test(i32* %P) {
@G2 = internal global i32* null ; <i32**> [#uses=3]
declare i8* @calloc(i32, i32)
declare noalias i8* @calloc(i32, i32)
define void @calloc_init() {
; CHECK-LABEL: @calloc_init(
; CHECK-NEXT: [[A:%.*]] = call dereferenceable_or_null(4) i8* @calloc(i32 4, i32 1)
@ -80,12 +80,8 @@ define void @my_alloc_init() {
define i32 @my_alloc_test(i32* %P) {
; CHECK-LABEL: @my_alloc_test(
; CHECK-NEXT: [[G1:%.*]] = load i32*, i32** @G3, align 8
; CHECK-NEXT: [[H1:%.*]] = load i32, i32* [[G1]], align 4
; CHECK-NEXT: store i32 123, i32* [[P:%.*]], align 4
; CHECK-NEXT: [[H2:%.*]] = load i32, i32* [[G1]], align 4
; CHECK-NEXT: [[X:%.*]] = sub i32 [[H1]], [[H2]]
; CHECK-NEXT: ret i32 [[X]]
; CHECK-NEXT: ret i32 0
;
%g1 = load i32*, i32** @G3 ; <i32*> [#uses=2]
%h1 = load i32, i32* %g1 ; <i32> [#uses=1]