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[WebAssembly] Implement red zone for user stack
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Implements a mostly-conventional redzone for the userspace
stack. Because we have unsigned load/store offsets we continue to use a
local SP subtracted from the incoming SP but do not write it back to
memory.

Differential Revision: http://reviews.llvm.org/D17525

llvm-svn: 261662
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@dschuff
dschuff committed Feb 23, 2016
1 parent 1b9fae5 commit 4b3bb21
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Showing 3 changed files with 68 additions and 26 deletions.
28 changes: 23 additions & 5 deletions llvm/lib/Target/WebAssembly/WebAssemblyFrameLowering.cpp
View file
Expand Up @@ -34,7 +34,6 @@ using namespace llvm;

#define DEBUG_TYPE "wasm-frame-info"

// TODO: Implement a red zone?
// TODO: wasm64
// TODO: Emit TargetOpcode::CFI_INSTRUCTION instructions

Expand All @@ -59,6 +58,24 @@ bool WebAssemblyFrameLowering::hasReservedCallFrame(
return !MF.getFrameInfo()->hasVarSizedObjects();
}


/// Returns true if this function needs a local user-space stack pointer.
/// Unlike a machine stack pointer, the wasm user stack pointer is a global
/// variable, so it is loaded into a register in the prolog.
bool WebAssemblyFrameLowering::needsSP(const MachineFunction &MF,
const MachineFrameInfo &MFI) const {
return MFI.getStackSize() || MFI.adjustsStack() || hasFP(MF);
}

/// Returns true if the local user-space stack pointer needs to be written back
/// to memory by this function (this is not meaningful if needsSP is false). If
/// false, the stack red zone can be used and only a local SP is needed.
bool WebAssemblyFrameLowering::needsSPWriteback(
const MachineFunction &MF, const MachineFrameInfo &MFI) const {
return MFI.getStackSize() > RedZoneSize || MFI.hasCalls() ||
MF.getFunction()->hasFnAttribute(Attribute::NoRedZone);
}

static void writeSPToMemory(unsigned SrcReg, MachineFunction &MF,
MachineBasicBlock &MBB,
MachineBasicBlock::iterator &InsertPt,
Expand Down Expand Up @@ -88,7 +105,8 @@ void WebAssemblyFrameLowering::eliminateCallFramePseudoInstr(
assert(!I->getOperand(0).getImm() && hasFP(MF) &&
"Call frame pseudos should only be used for dynamic stack adjustment");
const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
if (I->getOpcode() == TII->getCallFrameDestroyOpcode()) {
if (I->getOpcode() == TII->getCallFrameDestroyOpcode() &&
needsSPWriteback(MF, *MF.getFrameInfo())) {
DebugLoc DL = I->getDebugLoc();
writeSPToMemory(WebAssembly::SP32, MF, MBB, I, DL);
}
Expand All @@ -103,8 +121,8 @@ void WebAssemblyFrameLowering::emitPrologue(MachineFunction &MF,
"WebAssembly should not have callee-saved registers");
auto *WFI = MF.getInfo<WebAssemblyFunctionInfo>();

if (!needsSP(MF, *MFI)) return;
uint64_t StackSize = MFI->getStackSize();
if (!StackSize && !MFI->adjustsStack() && !hasFP(MF)) return;

const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
auto &MRI = MF.getRegInfo();
Expand Down Expand Up @@ -152,7 +170,7 @@ void WebAssemblyFrameLowering::emitPrologue(MachineFunction &MF,
WebAssembly::FP32)
.addReg(WebAssembly::SP32);
}
if (StackSize) {
if (StackSize && needsSPWriteback(MF, *MFI)) {
writeSPToMemory(WebAssembly::SP32, MF, MBB, InsertPt, DL);
}
}
Expand All @@ -161,7 +179,7 @@ void WebAssemblyFrameLowering::emitEpilogue(MachineFunction &MF,
MachineBasicBlock &MBB) const {
auto *MFI = MF.getFrameInfo();
uint64_t StackSize = MFI->getStackSize();
if (!StackSize && !MFI->adjustsStack() && !hasFP(MF)) return;
if (!needsSP(MF, *MFI) || !needsSPWriteback(MF, *MFI)) return;
auto *WFI = MF.getInfo<WebAssemblyFunctionInfo>();
const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
auto &MRI = MF.getRegInfo();
Expand Down
8 changes: 8 additions & 0 deletions llvm/lib/Target/WebAssembly/WebAssemblyFrameLowering.h
View file
Expand Up @@ -19,9 +19,12 @@
#include "llvm/Target/TargetFrameLowering.h"

namespace llvm {
class MachineFrameInfo;

class WebAssemblyFrameLowering final : public TargetFrameLowering {
public:
static const size_t RedZoneSize = 128;

WebAssemblyFrameLowering()
: TargetFrameLowering(StackGrowsDown, /*StackAlignment=*/16,
/*LocalAreaOffset=*/0,
Expand All @@ -38,6 +41,11 @@ class WebAssemblyFrameLowering final : public TargetFrameLowering {

bool hasFP(const MachineFunction &MF) const override;
bool hasReservedCallFrame(const MachineFunction &MF) const override;

private:
bool needsSP(const MachineFunction &MF, const MachineFrameInfo &MFI) const;
bool needsSPWriteback(const MachineFunction &MF,
const MachineFrameInfo &MFI) const;
};

} // end namespace llvm
Expand Down
58 changes: 37 additions & 21 deletions llvm/test/CodeGen/WebAssembly/userstack.ll
View file
Expand Up @@ -5,10 +5,13 @@
target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
target triple = "wasm32-unknown-unknown"

declare void @ext_func(i64* %ptr)
declare void @ext_func_i32(i32* %ptr)

; CHECK-LABEL: alloca32:
; Check that there is an extra local for the stack pointer.
; CHECK: .local i32{{$}}
define void @alloca32() {
define void @alloca32() noredzone {
; CHECK: i32.const $push[[L1:.+]]=, __stack_pointer{{$}}
; CHECK-NEXT: i32.load $push[[L2:.+]]=, 0($pop[[L1]])
; CHECK-NEXT: i32.const $push[[L3:.+]]=, 16
Expand All @@ -33,20 +36,15 @@ define void @alloca3264() {
; CHECK-NEXT: i32.load $push[[L2:.+]]=, 0($pop[[L1]])
; CHECK-NEXT: i32.const $push[[L3:.+]]=, 16
; CHECK-NEXT: i32.sub [[SP:.+]]=, $pop[[L2]], $pop[[L3]]
; CHECK-NEXT: i32.const $push[[L4:.+]]=, __stack_pointer{{$}}
; CHECK-NEXT: i32.store $discard=, 0($pop[[L4]]), [[SP]]
%r1 = alloca i32
%r2 = alloca double
; CHECK: i32.const $push[[L3:.+]]=, 0
; CHECK: i32.store {{.*}}=, 12([[SP]]), $pop[[L3]]
; CHECK-NEXT: i32.const $push[[L3:.+]]=, 0
; CHECK-NEXT: i32.store {{.*}}=, 12([[SP]]), $pop[[L3]]
store i32 0, i32* %r1
; CHECK: i64.const $push[[L0:.+]]=, 0
; CHECK: i64.store {{.*}}=, 0([[SP]]), $pop[[L0]]
; CHECK-NEXT: i64.const $push[[L0:.+]]=, 0
; CHECK-NEXT: i64.store {{.*}}=, 0([[SP]]), $pop[[L0]]
store double 0.0, double* %r2
; CHECK: i32.const $push[[L5:.+]]=, 16
; CHECK-NEXT: i32.add [[SP]]=, [[SP]], $pop[[L5]]
; CHECK-NEXT: i32.const $push[[L6:.+]]=, __stack_pointer
; CHECK-NEXT: i32.store $discard=, 0($pop[[L6]]), [[SP]]
; CHECK-NEXT: return
ret void
}

Expand All @@ -55,11 +53,11 @@ define void @alloca3264() {
define void @allocarray() {
; CHECK: i32.const $push[[L1:.+]]=, __stack_pointer
; CHECK-NEXT: i32.load $push[[L2:.+]]=, 0($pop[[L1]])
; CHECK-NEXT: i32.const $push[[L3:.+]]=, 32{{$}}
; CHECK-NEXT: i32.const $push[[L3:.+]]=, 144{{$}}
; CHECK-NEXT: i32.sub [[SP:.+]]=, $pop[[L2]], $pop[[L3]]
; CHECK-NEXT: i32.const $push[[L4:.+]]=, __stack_pointer{{$}}
; CHECK-NEXT: i32.store $discard=, 0($pop[[L4]]), [[SP]]
%r = alloca [5 x i32]
%r = alloca [33 x i32]

; CHECK-NEXT: i32.const $push[[L4:.+]]=, 12
; CHECK-NEXT: i32.const [[L5:.+]]=, 12
Expand All @@ -68,19 +66,18 @@ define void @allocarray() {
; CHECK-NEXT: i32.const $push[[L9:.+]]=, 1{{$}}
; CHECK-NEXT: i32.store $push[[L10:.+]]=, 12([[SP]]), $pop[[L9]]{{$}}
; CHECK-NEXT: i32.store $discard=, 0($pop3), $pop[[L10]]{{$}}
%p = getelementptr [5 x i32], [5 x i32]* %r, i32 0, i32 0
%p = getelementptr [33 x i32], [33 x i32]* %r, i32 0, i32 0
store i32 1, i32* %p
%p2 = getelementptr [5 x i32], [5 x i32]* %r, i32 0, i32 3
%p2 = getelementptr [33 x i32], [33 x i32]* %r, i32 0, i32 3
store i32 1, i32* %p2

; CHECK: i32.const $push[[L11:.+]]=, 32
; CHECK: i32.const $push[[L11:.+]]=, 144
; CHECK-NEXT: i32.add [[SP]]=, [[SP]], $pop[[L11]]
; CHECK-NEXT: i32.const $push[[L12:.+]]=, __stack_pointer
; CHECK-NEXT: i32.store $discard=, 0($pop[[L12]]), [[SP]]
ret void
}

declare void @ext_func(i64* %ptr)
; CHECK-LABEL: non_mem_use
define void @non_mem_use(i8** %addr) {
; CHECK: i32.const $push[[L1:.+]]=, 48
Expand Down Expand Up @@ -122,6 +119,7 @@ define void @allocarray_inbounds() {
; CHECK-NEXT: i32.store {{.*}}=, 24([[SP]]), $pop
%p2 = getelementptr inbounds [5 x i32], [5 x i32]* %r, i32 0, i32 3
store i32 1, i32* %p2
call void @ext_func(i64* null);
; CHECK: i32.const $push[[L5:.+]]=, 32
; CHECK-NEXT: i32.add [[SP]]=, [[SP]], $pop[[L5]]
; CHECK-NEXT: i32.const $push[[L6:.+]]=, __stack_pointer
Expand All @@ -142,14 +140,32 @@ define void @dynamic_alloca(i32 %alloc) {
; CHECK-NEXT: i32.store $discard=, 0($pop[[L4]]), [[SP]]
%r = alloca i32, i32 %alloc
; Target-independent codegen also calculates the store addr
store i32 0, i32* %r
; CHECK: call ext_func_i32@FUNCTION
call void @ext_func_i32(i32* %r)
; CHECK: i32.const $push[[L3:.+]]=, __stack_pointer
; CHECK-NEXT: i32.store [[SP]]=, 0($pop[[L3]]), [[FP]]
ret void
}

; CHECK-LABEL: dynamic_alloca_redzone:
define void @dynamic_alloca_redzone(i32 %alloc) {
; CHECK: i32.const $push[[L1:.+]]=, __stack_pointer
; CHECK-NEXT: i32.load [[SP:.+]]=, 0($pop[[L1]])
; CHECK-NEXT: copy_local [[FP:.+]]=, [[SP]]
; Target independent codegen bumps the stack pointer
; CHECK: i32.sub [[R:.+]]=,
; CHECK-NEXT: copy_local [[SP]]=, [[R]]
%r = alloca i32, i32 %alloc
; check-next here asserts that SP is not written back.
; CHECK-NEXT: i32.const $push[[ZERO:.+]]=, 0
; CHECK-NEXT: i32.store $discard=, 0([[R]]), $pop[[ZERO]]
store i32 0, i32* %r
; CHECK-NEXT: return
ret void
}

; CHECK-LABEL: dynamic_static_alloca:
define void @dynamic_static_alloca(i32 %alloc) {
define void @dynamic_static_alloca(i32 %alloc) noredzone {
; Decrement SP in the prolog by the static amount and writeback to memory.
; CHECK: i32.const $push[[L1:.+]]=, __stack_pointer
; CHECK-NEXT: i32.load $push[[L2:.+]]=, 0($pop[[L1]])
Expand Down Expand Up @@ -204,8 +220,8 @@ declare i8* @llvm.frameaddress(i32)
; CHECK-NEXT: i32.load [[SP:.+]]=, 0($pop[[L1]])
; CHECK-NEXT: copy_local [[FP:.+]]=, [[SP]]
; CHECK-NEXT: call use_i8_star@FUNCTION, [[FP]]
; CHECK-NEXT: i32.const $push[[L6:.+]]=, __stack_pointer
; CHECK-NEXT: i32.store [[SP]]=, 0($pop[[L6]]), [[FP]]
; CHEC K-NEXT: i32.const $push[[L6:.+]]=, __stack_pointer
; CHEC K-NEXT: i32.store [[SP]]=, 0($pop[[L6]]), [[FP]]
define void @frameaddress_0() {
%t = call i8* @llvm.frameaddress(i32 0)
call void @use_i8_star(i8* %t)
Expand Down

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