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[GlobalOpt] Test array indices inside structs for out-of-bounds accesses 

We now, from clang, can turn arrays of
  static short g_data[] = {16, 16, 16, 16, 16, 16, 16, 16, 0, 0, 0, 0, 0, 0, 0, 0};
into structs of the form
  @g_data = internal global <{ [8 x i16], [8 x i16] }> ...

GlobalOpt will incorrectly SROA it, not realising that the access to the first
element may overflow into the second. This fixes it by checking geps more
thoroughly.

I believe this makes the globalsra-partial.ll test case invalid as the %i value
could be out of bounds. I've re-purposed it as a negative test for this case.

Differential Revision: https://reviews.llvm.org/D49816

llvm-svn: 338192
This commit is contained in:
David Green 2018-07-28 08:20:10 +00:00
parent f947608ddf
commit fc4b0fe0a2
3 changed files with 66 additions and 73 deletions
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118
llvm/lib/Transforms/IPO/GlobalOpt.cpp
View File

@ -357,6 +357,41 @@ static bool CleanupConstantGlobalUsers(Value *V, Constant *Init,
return Changed;
}
static bool isSafeSROAElementUse(Value *V);
/// Return true if the specified GEP is a safe user of a derived
/// expression from a global that we want to SROA.
static bool isSafeSROAGEP(User *U) {
// Check to see if this ConstantExpr GEP is SRA'able. In particular, we
// don't like < 3 operand CE's, and we don't like non-constant integer
// indices. This enforces that all uses are 'gep GV, 0, C, ...' for some
// value of C.
if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) ||
!cast<Constant>(U->getOperand(1))->isNullValue())
return false;
gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U);
++GEPI; // Skip over the pointer index.
// For all other level we require that the indices are constant and inrange.
// In particular, consider: A[0][i]. We cannot know that the user isn't doing
// invalid things like allowing i to index an out-of-range subscript that
// accesses A[1]. This can also happen between different members of a struct
// in llvm IR.
for (; GEPI != E; ++GEPI) {
if (GEPI.isStruct())
continue;
ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand());
if (!IdxVal || (GEPI.isBoundedSequential() &&
IdxVal->getZExtValue() >= GEPI.getSequentialNumElements()))
return false;
}
return llvm::all_of(U->users(),
[](User *UU) { return isSafeSROAElementUse(UU); });
}
/// Return true if the specified instruction is a safe user of a derived
/// expression from a global that we want to SROA.
static bool isSafeSROAElementUse(Value *V) {
@ -374,84 +409,25 @@ static bool isSafeSROAElementUse(Value *V) {
if (StoreInst *SI = dyn_cast<StoreInst>(I))
return SI->getOperand(0) != V;
// Otherwise, it must be a GEP.
GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I);
if (!GEPI) return false;
if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) ||
!cast<Constant>(GEPI->getOperand(1))->isNullValue())
return false;
for (User *U : GEPI->users())
if (!isSafeSROAElementUse(U))
return false;
return true;
}
/// U is a direct user of the specified global value. Look at it and its uses
/// and decide whether it is safe to SROA this global.
static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) {
// The user of the global must be a GEP Inst or a ConstantExpr GEP.
if (!isa<GetElementPtrInst>(U) &&
(!isa<ConstantExpr>(U) ||
cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr))
return false;
// Check to see if this ConstantExpr GEP is SRA'able. In particular, we
// don't like < 3 operand CE's, and we don't like non-constant integer
// indices. This enforces that all uses are 'gep GV, 0, C, ...' for some
// value of C.
if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) ||
!cast<Constant>(U->getOperand(1))->isNullValue() ||
!isa<ConstantInt>(U->getOperand(2)))
return false;
gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U);
++GEPI; // Skip over the pointer index.
// If this is a use of an array allocation, do a bit more checking for sanity.
if (GEPI.isSequential()) {
ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2));
// Check to make sure that index falls within the array. If not,
// something funny is going on, so we won't do the optimization.
//
if (GEPI.isBoundedSequential() &&
Idx->getZExtValue() >= GEPI.getSequentialNumElements())
return false;
// We cannot scalar repl this level of the array unless any array
// sub-indices are in-range constants. In particular, consider:
// A[0][i]. We cannot know that the user isn't doing invalid things like
// allowing i to index an out-of-range subscript that accesses A[1].
//
// Scalar replacing *just* the outer index of the array is probably not
// going to be a win anyway, so just give up.
for (++GEPI; // Skip array index.
GEPI != E;
++GEPI) {
if (GEPI.isStruct())
continue;
ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand());
if (!IdxVal ||
(GEPI.isBoundedSequential() &&
IdxVal->getZExtValue() >= GEPI.getSequentialNumElements()))
return false;
}
}
return llvm::all_of(U->users(),
[](User *UU) { return isSafeSROAElementUse(UU); });
// Otherwise, it must be a GEP. Check it and its users are safe to SRA.
return isa<GetElementPtrInst>(I) && isSafeSROAGEP(I);
}
/// Look at all uses of the global and decide whether it is safe for us to
/// perform this transformation.
static bool GlobalUsersSafeToSRA(GlobalValue *GV) {
for (User *U : GV->users())
if (!IsUserOfGlobalSafeForSRA(U, GV))
for (User *U : GV->users()) {
// The user of the global must be a GEP Inst or a ConstantExpr GEP.
if (!isa<GetElementPtrInst>(U) &&
(!isa<ConstantExpr>(U) ||
cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr))
return false;
// Check the gep and it's users are safe to SRA
if (!isSafeSROAGEP(U))
return false;
}
return true;
}

16
llvm/test/Transforms/GlobalOpt/globalsra-multigep.ll Normal file
View File

@ -0,0 +1,16 @@
; RUN: opt < %s -globalopt -S | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@g_data = internal unnamed_addr global <{ [8 x i16], [8 x i16] }> <{ [8 x i16] [i16 16, i16 16, i16 16, i16 16, i16 16, i16 16, i16 16, i16 16], [8 x i16] zeroinitializer }>, align 16
; We cannot SRA here due to the second gep meaning the access to g_data may be to either element
; CHECK: @g_data = internal unnamed_addr constant <{ [8 x i16], [8 x i16] }>
define i16 @test(i64 %a1) {
entry:
%g1 = getelementptr inbounds <{ [8 x i16], [8 x i16] }>, <{ [8 x i16], [8 x i16] }>* @g_data, i64 0, i32 0
%arrayidx.i = getelementptr inbounds [8 x i16], [8 x i16]* %g1, i64 0, i64 %a1
%r = load i16, i16* %arrayidx.i, align 2
ret i16 %r
}

5
llvm/test/Transforms/GlobalOpt/globalsra-partial.ll
View File

@ -1,11 +1,12 @@
; In this case, the global can only be broken up by one level.
; In this case, the global cannot be merged as i may be out of range
; RUN: opt < %s -globalopt -S | FileCheck %s
target datalayout = "E-p:64:64:64-a0:0:8-f32:32:32-f64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-v64:64:64-v128:128:128"
@G = internal global { i32, [4 x float] } zeroinitializer ; <{ i32, [4 x float] }*> [#uses=3]
; CHECK-NOT: 12345
; CHECK: @G = internal unnamed_addr global { i32, [4 x float] }
; CHECK: 12345
define void @onlystore() {
store i32 12345, i32* getelementptr ({ i32, [4 x float] }, { i32, [4 x float] }* @G, i32 0, i32 0)
ret void