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[deref] Handle byval/byref/sret/inalloc/preallocated arguments for deref-at-point semantics 

All of these are scoped allocations which remain dereferenceable during the lifetime of the callee.

Differential Revision: https://reviews.llvm.org/D99310
This commit is contained in:
Philip Reames 2021-03-25 14:47:31 -07:00
parent 67e28173f1
commit e7ebb87222
2 changed files with 18 additions and 12 deletions
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6
llvm/lib/IR/Value.cpp
View File

@ -739,6 +739,12 @@ static bool canBeFreed(const Value *V) {
if (isa<Constant>(V))
return false;
// Handle byval/byref/sret/inalloca/preallocated arguments. The storage
// lifetime is guaranteed to be longer than the callee's lifetime.
if (auto *A = dyn_cast<Argument>(V))
if (A->hasPointeeInMemoryValueAttr())
return false;
const Function *F = nullptr;
if (auto *I = dyn_cast<Instruction>(V))
F = I->getFunction();

24
llvm/test/Analysis/ValueTracking/memory-dereferenceable.ll
View File

@ -25,8 +25,7 @@ declare i32* @foo()
; Loads from sret arguments
; CHECK-LABEL: 'test_sret'
; GLOBAL: %sret_gep{{.*}}(aligned)
; POINT-NOT: %sret_gep{{.*}}(aligned)
; CHECK: %sret_gep{{.*}}(aligned)
; CHECK-NOT: %sret_gep_outside
define void @test_sret(%struct.A* sret(%struct.A) %result) {
%sret_gep = getelementptr inbounds %struct.A, %struct.A* %result, i64 0, i32 1, i64 2
@ -210,22 +209,23 @@ define void @global_allocationsize() {
; Loads from byval arguments
; CHECK-LABEL: 'byval'
; GLOBAL: %i8_byval{{.*}}(aligned)
; POINT-NOT: %i8_byval{{.*}}(aligned)
; CHECK-NOT: %byval_cast
; GLOBAL: %byval_gep{{.*}}(aligned)
; POINT-NOT: %byval_gep{{.*}}(aligned)
; FIXME: Should hold in the point semantics case too
; CHECK: %i8_byval{{.*}}(aligned)
; CHECK-NOT: %bad_byval_cast
; CHECK: %byval_gep{{.*}}(aligned)
; CHECK: %good_byval_cast{{.*}}(unaligned)
define void @byval(i8* byval(i8) %i8_byval,
%struct.A* byval(%struct.A) %A_byval) {
%struct.A* byval(%struct.A) %A_byval) {
call void @mayfree()
%i8_byval_load = load i8, i8* %i8_byval
load i8, i8* %i8_byval
%byval_cast = bitcast i8* %i8_byval to i32*
%bad_byval_load = load i32, i32* %byval_cast
%bad_byval_cast = bitcast i8* %i8_byval to i32*
load i32, i32* %bad_byval_cast
%byval_gep = getelementptr inbounds %struct.A, %struct.A* %A_byval, i64 0, i32 1, i64 2
load i8, i8* %byval_gep
%good_byval_cast = bitcast %struct.A* %A_byval to i32*
load i32, i32* %good_byval_cast
ret void
}