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[WebAssembly] Support frame pointer 

Add support for frame pointer use in prolog/epilog.
Supports dynamic allocas but not yet over-aligned locals.
Target-independend CG generates SP updates, but we still need to write
back the SP value to memory when necessary.

llvm-svn: 259220
This commit is contained in:
Derek Schuff 2016-01-29 18:37:49 +00:00
parent 0df98ff913
commit 6ea637af35
4 changed files with 112 additions and 20 deletions
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90
llvm/lib/Target/WebAssembly/WebAssemblyFrameLowering.cpp
View File

@ -70,6 +70,7 @@ static void adjustStackPointer(unsigned StackSize,
const TargetInstrInfo* TII,
MachineBasicBlock::iterator InsertPt,
const DebugLoc& DL) {
assert((StackSize || !AdjustUp) && "Adjusting up by 0");
auto &MRI = MF.getRegInfo();
unsigned SPReg = MRI.createVirtualRegister(&WebAssembly::I32RegClass);
auto *SPSymbol = MF.createExternalSymbolName("__stack_pointer");
@ -82,8 +83,8 @@ static void adjustStackPointer(unsigned StackSize,
auto *LoadMMO = new MachineMemOperand(MachinePointerInfo(),
MachineMemOperand::MOLoad, 4, 4);
BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::LOAD_I32), SPReg)
.addImm(0)
.addReg(SPReg)
.addImm(0) // offset
.addReg(SPReg) // addr
.addImm(2) // p2align
.addMemOperand(LoadMMO);
// Add/Subtract the frame size
@ -116,6 +117,9 @@ void WebAssemblyFrameLowering::eliminateCallFramePseudoInstr(
unsigned Opc = I->getOpcode();
bool IsDestroy = Opc == TII->getCallFrameDestroyOpcode();
unsigned Amount = I->getOperand(0).getImm();
// TODO(dschuff): After we switch varargs to passing an explicit pointer
// rather than using an implicit call frame, assert here that Amount is 0
// and remove adjustStackPointer altogether.
if (Amount)
adjustStackPointer(Amount, IsDestroy, MF, MBB,
TII, I, DL);
@ -128,23 +132,76 @@ void WebAssemblyFrameLowering::emitPrologue(MachineFunction &MF,
auto *MFI = MF.getFrameInfo();
assert(MFI->getCalleeSavedInfo().empty() &&
"WebAssembly should not have callee-saved registers");
assert(!hasFP(MF) && "Functions needing frame pointers not yet supported");
uint64_t StackSize = MFI->getStackSize();
if (!StackSize && (!MFI->adjustsStack() || MFI->getMaxCallFrameSize() == 0))
if (!StackSize && !MFI->adjustsStack())
return;
const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
auto &MRI = MF.getRegInfo();
auto InsertPt = MBB.begin();
DebugLoc DL;
adjustStackPointer(StackSize, false, MF, MBB, TII, InsertPt, DL);
unsigned SPReg = MRI.createVirtualRegister(&WebAssembly::I32RegClass);
auto *SPSymbol = MF.createExternalSymbolName("__stack_pointer");
BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), SPReg)
.addExternalSymbol(SPSymbol);
// This MachinePointerInfo should reference __stack_pointer as well but
// doesn't because MachinePointerInfo() takes a GV which we don't have for
// __stack_pointer. TODO: check if PseudoSourceValue::ExternalSymbolCallEntry
// is appropriate instead. (likewise for EmitEpologue below)
auto *LoadMMO = new MachineMemOperand(MachinePointerInfo(),
MachineMemOperand::MOLoad, 4, 4);
// Load the SP value.
BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::LOAD_I32),
StackSize ? SPReg : WebAssembly::SP32)
.addImm(0) // offset
.addReg(SPReg) // addr
.addImm(2) // p2align
.addMemOperand(LoadMMO);
unsigned OffsetReg = 0;
if (StackSize) {
// Subtract the frame size
OffsetReg = MRI.createVirtualRegister(&WebAssembly::I32RegClass);
BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), OffsetReg)
.addImm(StackSize);
BuildMI(MBB, InsertPt, DL,
TII->get(WebAssembly::SUB_I32),
WebAssembly::SP32)
.addReg(SPReg)
.addReg(OffsetReg);
}
if (hasFP(MF)) {
// Unlike most conventional targets (where FP points to the saved FP),
// FP points to the bottom of the fixed-size locals, so we can use positive
// offsets in load/store instructions.
BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::COPY_LOCAL_I32),
WebAssembly::FP32)
.addReg(WebAssembly::SP32);
}
if (StackSize) {
assert(OffsetReg);
// The SP32 register now has the new stacktop. Also write it back to memory.
BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), OffsetReg)
.addExternalSymbol(SPSymbol);
auto *MMO = new MachineMemOperand(MachinePointerInfo(),
MachineMemOperand::MOStore, 4, 4);
BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::STORE_I32), WebAssembly::SP32)
.addImm(0)
.addReg(OffsetReg)
.addImm(2) // p2align
.addReg(WebAssembly::SP32)
.addMemOperand(MMO);
}
}
void WebAssemblyFrameLowering::emitEpilogue(MachineFunction &MF,
MachineBasicBlock &MBB) const {
uint64_t StackSize = MF.getFrameInfo()->getStackSize();
if (!StackSize)
auto *MFI = MF.getFrameInfo();
uint64_t StackSize = MFI->getStackSize();
if (!StackSize && !MFI->adjustsStack())
return;
const auto *TII = MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
auto &MRI = MF.getRegInfo();
@ -156,14 +213,17 @@ void WebAssemblyFrameLowering::emitEpilogue(MachineFunction &MF,
DL = InsertPt->getDebugLoc();
}
// Restore the stack pointer. Without FP its value is just SP32 - stacksize
BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), OffsetReg)
.addImm(StackSize);
// Restore the stack pointer. If we had fixed-size locals, add the offset
// subtracted in the prolog.
if (StackSize) {
BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), OffsetReg)
.addImm(StackSize);
BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::ADD_I32), WebAssembly::SP32)
.addReg(hasFP(MF) ? WebAssembly::FP32 : WebAssembly::SP32)
.addReg(OffsetReg);
}
auto *SPSymbol = MF.createExternalSymbolName("__stack_pointer");
// TODO: Fold this add into the const offset field of the store.
BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::ADD_I32), WebAssembly::SP32)
.addReg(WebAssembly::SP32)
.addReg(OffsetReg);
// Re-use OffsetReg to hold the address of the stacktop
BuildMI(MBB, InsertPt, DL, TII->get(WebAssembly::CONST_I32), OffsetReg)
.addExternalSymbol(SPSymbol);
@ -173,6 +233,6 @@ void WebAssemblyFrameLowering::emitEpilogue(MachineFunction &MF,
.addImm(0)
.addReg(OffsetReg)
.addImm(2) // p2align
.addReg(WebAssembly::SP32)
.addReg((!StackSize && hasFP(MF)) ? WebAssembly::FP32 : WebAssembly::SP32)
.addMemOperand(MMO);
}

2
llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.cpp
View File

@ -58,7 +58,7 @@ void WebAssemblyInstrInfo::copyPhysReg(MachineBasicBlock &MBB,
const TargetRegisterClass *RC =
TargetRegisterInfo::isVirtualRegister(DestReg)
? MRI.getRegClass(DestReg)
: MRI.getTargetRegisterInfo()->getMinimalPhysRegClass(SrcReg);
: MRI.getTargetRegisterInfo()->getMinimalPhysRegClass(DestReg);
unsigned CopyLocalOpcode;
if (RC == &WebAssembly::I32RegClass)

7
llvm/lib/Target/WebAssembly/WebAssemblyRegNumbering.cpp
View File

@ -108,10 +108,15 @@ bool WebAssemblyRegNumbering::runOnMachineFunction(MachineFunction &MF) {
}
}
// Allocate locals for used physical registers
if (FrameInfo.getStackSize() > 0) {
if (FrameInfo.getStackSize() > 0 || FrameInfo.adjustsStack()) {
DEBUG(dbgs() << "PReg SP " << CurReg << "\n");
MFI.addPReg(WebAssembly::SP32, CurReg++);
}
bool HasFP = MF.getSubtarget().getFrameLowering()->hasFP(MF);
if (HasFP) {
DEBUG(dbgs() << "PReg FP " << CurReg << "\n");
MFI.addPReg(WebAssembly::FP32, CurReg++);
}
return true;
}

33
llvm/test/CodeGen/WebAssembly/userstack.ll
View File

@ -119,9 +119,36 @@ define void @allocarray_inbounds() {
; CHECK-LABEL: dynamic_alloca:
define void @dynamic_alloca(i32 %alloc) {
; TODO: Support frame pointers
;%r = alloca i32, i32 %alloc
;store i32 0, i32* %r
; CHECK: i32.const [[L0:.+]]=, __stack_pointer
; CHECK-NEXT: i32.load [[SP:.+]]=, 0([[L0]])
; CHECK-NEXT: copy_local [[FP:.+]]=, [[SP]]
; Target independent codegen bumps the stack pointer
; FIXME: we need to write the value back to memory
%r = alloca i32, i32 %alloc
; Target-independent codegen also calculates the store addr
store i32 0, i32* %r
; CHECK: i32.const [[L3:.+]]=, __stack_pointer
; CHECK-NEXT: i32.store [[SP]]=, 0([[L3]]), [[FP]]
ret void
}
; CHECK-LABEL: dynamic_static_alloca:
define void @dynamic_static_alloca(i32 %alloc) {
; CHECK: i32.const [[L0:.+]]=, __stack_pointer
; CHECK-NEXT: i32.load [[L0]]=, 0([[L0]])
; CHECK-NEXT: i32.const [[L2:.+]]=, 16
; CHECK-NEXT: i32.sub [[SP:.+]]=, [[L0]], [[L2]]
; CHECK-NEXT: copy_local [[FP:.+]]=, [[SP]]
; CHECK-NEXT: i32.const [[L3:.+]]=, __stack_pointer
; CHECK-NEXT: i32.store {{.*}}=, 0([[L3]]), [[SP]]
%r1 = alloca i32
%r = alloca i32, i32 %alloc
store i32 0, i32* %r
; CHECK: i32.const [[L3:.+]]=, 16
; CHECK: i32.add [[SP]]=, [[FP]], [[L3]]
; CHECK: i32.const [[L4:.+]]=, __stack_pointer
; CHECK-NEXT: i32.store [[SP]]=, 0([[L4]]), [[SP]]
ret void
}
; TODO: test aligned alloc