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Recommit "[SCCP] Do not replace deref'able ptr with un-deref'able one." 

This version includes an small fix allowing function pointers to be
unconditionally replaced for now.

This reverts commit 4c5e4aa89b.
This commit is contained in:
Florian Hahn 2020-09-28 16:08:30 +01:00
parent 4c19b89b25
commit 86a20d9e34
5 changed files with 43 additions and 5 deletions
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4
llvm/lib/Analysis/Loads.cpp
View File

@ -510,6 +510,10 @@ bool llvm::canReplacePointersIfEqual(Value *A, Value *B, const DataLayout &DL,
assert(Ty == B->getType() && Ty->isPointerTy() &&
"values must have matching pointer types");
// Function pointers are not directly dereferenced using load/store
// instructions. Allow any replacements for now.
if (A->getType()->getPointerElementType()->isFunctionTy())
return true;
// NOTE: The checks in the function are incomplete and currently miss illegal
// cases! The current implementation is a starting point and the
// implementation should be made stricter over time.

11
llvm/lib/Transforms/Scalar/SCCP.cpp
View File

@ -31,6 +31,7 @@
#include "llvm/Analysis/DomTreeUpdater.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueLattice.h"
#include "llvm/Analysis/ValueLatticeUtils.h"
@ -177,6 +178,8 @@ class SCCPSolver : public InstVisitor<SCCPSolver> {
LLVMContext &Ctx;
public:
const DataLayout &getDataLayout() const { return DL; }
void addAnalysis(Function &F, AnalysisResultsForFn A) {
AnalysisResults.insert({&F, std::move(A)});
}
@ -1649,6 +1652,14 @@ static bool tryToReplaceWithConstant(SCCPSolver &Solver, Value *V) {
return false;
}
// Do not propagate equality of a un-dereferenceable pointer.
// FIXME: Currently this only treats pointers one past the last element
// for array types. Should probably be much stricter.
if (Const->getType()->isPointerTy() &&
!canReplacePointersIfEqual(V, Const, Solver.getDataLayout(),
dyn_cast<Instruction>(V)))
return false;
LLVM_DEBUG(dbgs() << " Constant: " << *Const << " = " << *V << '\n');
// Replaces all of the uses of a variable with uses of the constant.

6
llvm/test/Transforms/SCCP/apint-bigint2.ll
View File

@ -51,8 +51,10 @@ define i101 @large_aggregate_2() {
}
; CHECK-LABEL: @index_too_large
; CHECK-NEXT: store i101* getelementptr (i101, i101* getelementptr ([6 x i101], [6 x i101]* @Y, i32 0, i32 -1), i101 9224497936761618431), i101** undef
; CHECK-NEXT: ret void
; CHECK-NEXT: %ptr1 = getelementptr [6 x i101], [6 x i101]* @Y, i32 0, i32 -1
; CHECK-NEXT: %ptr2 = getelementptr i101, i101* %ptr1, i101 9224497936761618431
; CHECK-NEXT: store i101* %ptr2, i101** undef
; CHECK-NEXT: ret void
define void @index_too_large() {
%ptr1 = getelementptr [6 x i101], [6 x i101]* @Y, i32 0, i32 -1
%ptr2 = getelementptr i101, i101* %ptr1, i101 9224497936761618431

4
llvm/test/Transforms/SCCP/indirectbr.ll
View File

@ -31,7 +31,9 @@ BB1:
define void @indbrtest2() {
; CHECK-LABEL: @indbrtest2(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[BB1:%.*]]
; CHECK-NEXT: [[B:%.*]] = inttoptr i64 ptrtoint (i8* blockaddress(@indbrtest2, [[BB1:%.*]]) to i64) to i8*
; CHECK-NEXT: [[C:%.*]] = bitcast i8* [[B]] to i8*
; CHECK-NEXT: br label [[BB1]]
; CHECK: BB1:
; CHECK-NEXT: call void @BB1_f()
; CHECK-NEXT: ret void

23
llvm/test/Transforms/SCCP/replace-dereferenceable-ptr-with-undereferenceable.ll
View File

@ -11,7 +11,7 @@ define i32 @eq_undereferenceable(i32* %p) {
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32* [[P:%.*]], getelementptr inbounds (i32, i32* getelementptr inbounds ([1 x i32], [1 x i32]* @x, i64 0, i64 0), i64 1)
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
; CHECK: if.then:
; CHECK-NEXT: store i32 2, i32* getelementptr inbounds (i32, i32* getelementptr inbounds ([1 x i32], [1 x i32]* @x, i64 0, i64 0), i64 1), align 4
; CHECK-NEXT: store i32 2, i32* [[P]], align 4
; CHECK-NEXT: br label [[IF_END]]
; CHECK: if.end:
; CHECK-NEXT: [[TMP0:%.*]] = load i32, i32* getelementptr inbounds ([1 x i32], [1 x i32]* @y, i64 0, i64 0), align 4
@ -65,7 +65,7 @@ define i1 @eq_undereferenceable_cmp_simp(i32* %p) {
; CHECK-NEXT: [[CMP_0:%.*]] = icmp eq i32* [[P:%.*]], getelementptr inbounds (i32, i32* getelementptr inbounds ([1 x i32], [1 x i32]* @x, i64 0, i64 0), i64 1)
; CHECK-NEXT: br i1 [[CMP_0]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
; CHECK: if.then:
; CHECK-NEXT: store i32 2, i32* getelementptr inbounds (i32, i32* getelementptr inbounds ([1 x i32], [1 x i32]* @x, i64 0, i64 0), i64 1), align 4
; CHECK-NEXT: store i32 2, i32* [[P]], align 4
; CHECK-NEXT: ret i1 true
; CHECK: if.end:
; CHECK-NEXT: [[CMP_2:%.*]] = icmp eq i32* [[P]], getelementptr inbounds (i32, i32* getelementptr inbounds ([1 x i32], [1 x i32]* @x, i64 0, i64 0), i64 1)
@ -84,3 +84,22 @@ if.end: ; preds = %if.then, %entry
%cmp.2 = icmp eq i32* %p, getelementptr inbounds (i32, i32* getelementptr inbounds ([1 x i32], [1 x i32]* @x, i64 0, i64 0), i64 1)
ret i1 %cmp.2
}
; Test cases with function pointers. Currently any replacements are allowed
; for them.
@FnGlobal1 = internal global void (i8*)* undef, align 8
define void (i8*)* @test_global_undef_fn_ptr() {
%lv = load void (i8*)*, void (i8*)** @FnGlobal1, align 8
ret void (i8*)* %lv
}
declare void @foo(i8*)
@FnGlobal2 = internal global void (i8*)* @foo, align 8
define void (i8*)* @test_global_undef_fn_ptr2() {
%lv = load void (i8*)*, void (i8*)** @FnGlobal2, align 8
ret void (i8*)* %lv
}