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X86: Avoid using _chkstk when lowering WIN_ALLOCA instructions

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This patch moves the expansion of WIN_ALLOCA pseudo-instructions
into a separate pass that walks the CFG and lowers the instructions
based on a conservative estimate of the offset between the stack
pointer and the lowest accessed stack address.

The goal is to reduce binary size and run-time costs by removing
calls to _chkstk. While it doesn't fix all the code quality problems
with inalloca calls, it's an incremental improvement for PR27076.

Differential Revision: http://reviews.llvm.org/D20263

llvm-svn: 269828
This commit is contained in:
Hans Wennborg 2016-05-17 20:13:29 +00:00
parent bed075aa5a
commit 09bf3bedad
17 changed files with 502 additions and 54 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
lib/Target/X86/CMakeLists.txt
View File

@ -37,6 +37,7 @@ set(sources
X86WinEHState.cpp
X86OptimizeLEAs.cpp
X86FixupBWInsts.cpp
X86WinAllocaExpander.cpp
)
add_llvm_target(X86CodeGen ${sources})

3
lib/Target/X86/X86.h
View File

@ -59,6 +59,9 @@ FunctionPass *createX86FixupLEAs();
/// recalculations.
FunctionPass *createX86OptimizeLEAs();
/// Return a pass that expands WinAlloca pseudo-instructions.
FunctionPass *createX86WinAllocaExpander();
/// Return a pass that optimizes the code-size of x86 call sequences. This is
/// done by replacing esp-relative movs with pushes.
FunctionPass *createX86CallFrameOptimization();

23
lib/Target/X86/X86ISelLowering.cpp
View File

@ -16563,14 +16563,9 @@ X86TargetLowering::LowerDYNAMIC_STACKALLOC(SDValue Op,
Result = DAG.getNode(X86ISD::SEG_ALLOCA, dl, SPTy, Chain,
DAG.getRegister(Vreg, SPTy));
} else {
SDValue Flag;
const unsigned Reg = (Subtarget.isTarget64BitLP64() ? X86::RAX : X86::EAX);
Chain = DAG.getCopyToReg(Chain, dl, Reg, Size, Flag);
Flag = Chain.getValue(1);
SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
Chain = DAG.getNode(X86ISD::WIN_ALLOCA, dl, NodeTys, Chain, Flag);
Chain = DAG.getNode(X86ISD::WIN_ALLOCA, dl, NodeTys, Chain, Size);
MF.getInfo<X86MachineFunctionInfo>()->setHasWinAlloca(true);
const X86RegisterInfo *RegInfo = Subtarget.getRegisterInfo();
unsigned SPReg = RegInfo->getStackRegister();
@ -23227,18 +23222,6 @@ X86TargetLowering::EmitLoweredSegAlloca(MachineInstr *MI,
return continueMBB;
}
MachineBasicBlock *
X86TargetLowering::EmitLoweredWinAlloca(MachineInstr *MI,
MachineBasicBlock *BB) const {
assert(!Subtarget.isTargetMachO());
DebugLoc DL = MI->getDebugLoc();
MachineInstr *ResumeMI = Subtarget.getFrameLowering()->emitStackProbe(
*BB->getParent(), *BB, MI, DL, false);
MachineBasicBlock *ResumeBB = ResumeMI->getParent();
MI->eraseFromParent(); // The pseudo instruction is gone now.
return ResumeBB;
}
MachineBasicBlock *
X86TargetLowering::EmitLoweredCatchRet(MachineInstr *MI,
MachineBasicBlock *BB) const {
@ -23701,8 +23684,6 @@ X86TargetLowering::EmitInstrWithCustomInserter(MachineInstr *MI,
case X86::TLS_base_addr32:
case X86::TLS_base_addr64:
return EmitLoweredTLSAddr(MI, BB);
case X86::WIN_ALLOCA:
return EmitLoweredWinAlloca(MI, BB);
case X86::CATCHRET:
return EmitLoweredCatchRet(MI, BB);
case X86::CATCHPAD:

3
lib/Target/X86/X86ISelLowering.h
View File

@ -1162,9 +1162,6 @@ namespace llvm {
MachineBasicBlock *EmitLoweredAtomicFP(MachineInstr *I,
MachineBasicBlock *BB) const;
MachineBasicBlock *EmitLoweredWinAlloca(MachineInstr *MI,
MachineBasicBlock *BB) const;
MachineBasicBlock *EmitLoweredCatchRet(MachineInstr *MI,
MachineBasicBlock *BB) const;

33
lib/Target/X86/X86InstrCompiler.td
View File

@ -99,18 +99,6 @@ def VAARG_64 : I<0, Pseudo,
(X86vaarg64 addr:$ap, imm:$size, imm:$mode, imm:$align)),
(implicit EFLAGS)]>;
// Dynamic stack allocation yields a _chkstk or _alloca call for all Windows
// targets. These calls are needed to probe the stack when allocating more than
// 4k bytes in one go. Touching the stack at 4K increments is necessary to
// ensure that the guard pages used by the OS virtual memory manager are
// allocated in correct sequence.
// The main point of having separate instruction are extra unmodelled effects
// (compared to ordinary calls) like stack pointer change.
let Defs = [EAX, ESP, EFLAGS], Uses = [ESP] in
def WIN_ALLOCA : I<0, Pseudo, (outs), (ins),
"# dynamic stack allocation",
[(X86WinAlloca)]>;
// When using segmented stacks these are lowered into instructions which first
// check if the current stacklet has enough free memory. If it does, memory is
@ -132,6 +120,27 @@ def SEG_ALLOCA_64 : I<0, Pseudo, (outs GR64:$dst), (ins GR64:$size),
Requires<[In64BitMode]>;
}
// Dynamic stack allocation yields a _chkstk or _alloca call for all Windows
// targets. These calls are needed to probe the stack when allocating more than
// 4k bytes in one go. Touching the stack at 4K increments is necessary to
// ensure that the guard pages used by the OS virtual memory manager are
// allocated in correct sequence.
// The main point of having separate instruction are extra unmodelled effects
// (compared to ordinary calls) like stack pointer change.
let Defs = [EAX, ESP, EFLAGS], Uses = [ESP] in
def WIN_ALLOCA_32 : I<0, Pseudo, (outs), (ins GR32:$size),
"# dynamic stack allocation",
[(X86WinAlloca GR32:$size)]>,
Requires<[NotLP64]>;
let Defs = [RAX, RSP, EFLAGS], Uses = [RSP] in
def WIN_ALLOCA_64 : I<0, Pseudo, (outs), (ins GR64:$size),
"# dynamic stack allocation",
[(X86WinAlloca GR64:$size)]>,
Requires<[In64BitMode]>;
//===----------------------------------------------------------------------===//
// EH Pseudo Instructions
//

6
lib/Target/X86/X86InstrInfo.td
View File

@ -112,6 +112,8 @@ def SDT_X86TLSBASEADDR : SDTypeProfile<0, 1, [SDTCisInt<0>]>;
def SDT_X86TLSCALL : SDTypeProfile<0, 1, [SDTCisInt<0>]>;
def SDT_X86WIN_ALLOCA : SDTypeProfile<0, 1, [SDTCisVT<0, iPTR>]>;
def SDT_X86SEG_ALLOCA : SDTypeProfile<1, 1, [SDTCisVT<0, iPTR>, SDTCisVT<1, iPTR>]>;
def SDT_X86EHRET : SDTypeProfile<0, 1, [SDTCisInt<0>]>;
@ -273,8 +275,8 @@ def X86bextr : SDNode<"X86ISD::BEXTR", SDTIntBinOp>;
def X86mul_imm : SDNode<"X86ISD::MUL_IMM", SDTIntBinOp>;
def X86WinAlloca : SDNode<"X86ISD::WIN_ALLOCA", SDTX86Void,
[SDNPHasChain, SDNPInGlue, SDNPOutGlue]>;
def X86WinAlloca : SDNode<"X86ISD::WIN_ALLOCA", SDT_X86WIN_ALLOCA,
[SDNPHasChain, SDNPOutGlue]>;
def X86SegAlloca : SDNode<"X86ISD::SEG_ALLOCA", SDT_X86SEG_ALLOCA,
[SDNPHasChain]>;

6
lib/Target/X86/X86MachineFunctionInfo.h
View File

@ -98,6 +98,9 @@ class X86MachineFunctionInfo : public MachineFunctionInfo {
/// True if this function uses the red zone.
bool UsesRedZone = false;
/// True if this function has WIN_ALLOCA instructions.
bool HasWinAlloca = false;
private:
/// ForwardedMustTailRegParms - A list of virtual and physical registers
/// that must be forwarded to every musttail call.
@ -172,6 +175,9 @@ public:
bool getUsesRedZone() const { return UsesRedZone; }
void setUsesRedZone(bool V) { UsesRedZone = V; }
bool hasWinAlloca() const { return HasWinAlloca; }
void setHasWinAlloca(bool v) { HasWinAlloca = v; }
};
} // End llvm namespace

1
lib/Target/X86/X86TargetMachine.cpp
View File

@ -266,6 +266,7 @@ void X86PassConfig::addPreRegAlloc() {
addPass(createX86OptimizeLEAs());
addPass(createX86CallFrameOptimization());
addPass(createX86WinAllocaExpander());
}
void X86PassConfig::addPostRegAlloc() {

294
lib/Target/X86/X86WinAllocaExpander.cpp Normal file
View File

@ -0,0 +1,294 @@
//===----- X86WinAllocaExpander.cpp - Expand WinAlloca pseudo instruction -===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines a pass that expands WinAlloca pseudo-instructions.
//
// It performs a conservative analysis to determine whether each allocation
// falls within a region of the stack that is safe to use, or whether stack
// probes must be emitted.
//
//===----------------------------------------------------------------------===//
#include "X86.h"
#include "X86InstrBuilder.h"
#include "X86InstrInfo.h"
#include "X86MachineFunctionInfo.h"
#include "X86Subtarget.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/IR/Function.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
using namespace llvm;
namespace {
class X86WinAllocaExpander : public MachineFunctionPass {
public:
X86WinAllocaExpander() : MachineFunctionPass(ID) {}
bool runOnMachineFunction(MachineFunction &MF) override;
private:
/// Strategies for lowering a WinAlloca.
enum Lowering { TouchAndSub, Sub, Probe };
/// Deterministic-order map from WinAlloca instruction to desired lowering.
typedef MapVector<MachineInstr*, Lowering> LoweringMap;
/// Compute which lowering to use for each WinAlloca instruction.
void computeLowerings(MachineFunction &MF, LoweringMap& Lowerings);
/// Get the appropriate lowering based on current offset and amount.
Lowering getLowering(int64_t CurrentOffset, int64_t AllocaAmount);
/// Lower a WinAlloca instruction.
void lower(MachineInstr* MI, Lowering L);
MachineRegisterInfo *MRI;
const X86Subtarget *STI;
const TargetInstrInfo *TII;
const X86RegisterInfo *TRI;
unsigned StackPtr;
unsigned SlotSize;
int64_t StackProbeSize;
const char *getPassName() const override { return "X86 WinAlloca Expander"; }
static char ID;
};
char X86WinAllocaExpander::ID = 0;
} // end anonymous namespace
FunctionPass *llvm::createX86WinAllocaExpander() {
return new X86WinAllocaExpander();
}
/// Return the allocation amount for a WinAlloca instruction, or -1 if unknown.
static int64_t getWinAllocaAmount(MachineInstr *MI, MachineRegisterInfo *MRI) {
assert(MI->getOpcode() == X86::WIN_ALLOCA_32 ||
MI->getOpcode() == X86::WIN_ALLOCA_64);
assert(MI->getOperand(0).isReg());
unsigned AmountReg = MI->getOperand(0).getReg();
MachineInstr *Def = MRI->getUniqueVRegDef(AmountReg);
// Look through copies.
while (Def && Def->isCopy() && Def->getOperand(1).isReg())
Def = MRI->getUniqueVRegDef(Def->getOperand(1).getReg());
if (!Def ||
(Def->getOpcode() != X86::MOV32ri && Def->getOpcode() != X86::MOV64ri) ||
!Def->getOperand(1).isImm())
return -1;
return Def->getOperand(1).getImm();
}
X86WinAllocaExpander::Lowering
X86WinAllocaExpander::getLowering(int64_t CurrentOffset,
int64_t AllocaAmount) {
// For a non-constant amount or a large amount, we have to probe.
if (AllocaAmount < 0 || AllocaAmount > StackProbeSize)
return Probe;
// If it fits within the safe region of the stack, just subtract.
if (CurrentOffset + AllocaAmount <= StackProbeSize)
return Sub;
// Otherwise, touch the current tip of the stack, then subtract.
return TouchAndSub;
}
static bool isPushPop(const MachineInstr &MI) {
switch (MI.getOpcode()) {
case X86::PUSH32i8:
case X86::PUSH32r:
case X86::PUSH32rmm:
case X86::PUSH32rmr:
case X86::PUSHi32:
case X86::PUSH64i8:
case X86::PUSH64r:
case X86::PUSH64rmm:
case X86::PUSH64rmr:
case X86::PUSH64i32:
case X86::POP32r:
case X86::POP64r:
return true;
default:
return false;
}
}
void X86WinAllocaExpander::computeLowerings(MachineFunction &MF,
LoweringMap &Lowerings) {
// Do a one-pass reverse post-order walk of the CFG to conservatively estimate
// the offset between the stack pointer and the lowest touched part of the
// stack, and use that to decide how to lower each WinAlloca instruction.
// Initialize OutOffset[B], the stack offset at exit from B, to something big.
DenseMap<MachineBasicBlock *, int64_t> OutOffset;
for (MachineBasicBlock &MBB : MF)
OutOffset[&MBB] = INT32_MAX;
// Note: we don't know the offset at the start of the entry block since the
// prologue hasn't been inserted yet, and how much that will adjust the stack
// pointer depends on register spills, which have not been computed yet.
// Compute the reverse post-order.
ReversePostOrderTraversal<MachineFunction*> RPO(&MF);
for (MachineBasicBlock *MBB : RPO) {
int64_t Offset = -1;
for (MachineBasicBlock *Pred : MBB->predecessors())
Offset = std::max(Offset, OutOffset[Pred]);
if (Offset == -1) Offset = INT32_MAX;
for (MachineInstr &MI : *MBB) {
if (MI.getOpcode() == X86::WIN_ALLOCA_32 ||
MI.getOpcode() == X86::WIN_ALLOCA_64) {
// A WinAlloca moves StackPtr, and potentially touches it.
int64_t Amount = getWinAllocaAmount(&MI, MRI);
Lowering L = getLowering(Offset, Amount);
Lowerings[&MI] = L;
switch (L) {
case Sub:
Offset += Amount;
break;
case TouchAndSub:
Offset = Amount;
break;
case Probe:
Offset = 0;
break;
}
} else if (MI.isCall() || isPushPop(MI)) {
// Calls, pushes and pops touch the tip of the stack.
Offset = 0;
} else if (MI.getOpcode() == X86::ADJCALLSTACKUP32 ||
MI.getOpcode() == X86::ADJCALLSTACKUP64) {
Offset -= MI.getOperand(0).getImm();
} else if (MI.getOpcode() == X86::ADJCALLSTACKDOWN32 ||
MI.getOpcode() == X86::ADJCALLSTACKDOWN64) {
Offset += MI.getOperand(0).getImm();
} else if (MI.modifiesRegister(StackPtr, TRI)) {
// Any other modification of SP means we've lost track of it.
Offset = INT32_MAX;
}
}
OutOffset[MBB] = Offset;
}
}
static unsigned getSubOpcode(bool Is64Bit, int64_t Amount) {
if (Is64Bit)
return isInt<8>(Amount) ? X86::SUB64ri8 : X86::SUB64ri32;
return isInt<8>(Amount) ? X86::SUB32ri8 : X86::SUB32ri;
}
void X86WinAllocaExpander::lower(MachineInstr* MI, Lowering L) {
DebugLoc DL = MI->getDebugLoc();
MachineBasicBlock *MBB = MI->getParent();
MachineBasicBlock::iterator I = *MI;
int64_t Amount = getWinAllocaAmount(MI, MRI);
if (Amount == 0) {
MI->eraseFromParent();
return;
}
bool Is64Bit = STI->is64Bit();
assert(SlotSize == 4 || SlotSize == 8);
unsigned RegA = (SlotSize == 8) ? X86::RAX : X86::EAX;
switch (L) {
case TouchAndSub:
assert(Amount >= SlotSize);
// Use a push to touch the top of the stack.
BuildMI(*MBB, I, DL, TII->get(Is64Bit ? X86::PUSH64r : X86::PUSH32r))
.addReg(RegA, RegState::Undef);
Amount -= SlotSize;
if (!Amount)
break;
// Fall through to make any remaining adjustment.
case Sub:
assert(Amount > 0);
if (Amount == SlotSize) {
// Use push to save size.
BuildMI(*MBB, I, DL, TII->get(Is64Bit ? X86::PUSH64r : X86::PUSH32r))
.addReg(RegA, RegState::Undef);
} else {
// Sub.
BuildMI(*MBB, I, DL, TII->get(getSubOpcode(Is64Bit, Amount)), StackPtr)
.addReg(StackPtr)
.addImm(Amount);
}
break;
case Probe:
// The probe lowering expects the amount in RAX/EAX.
BuildMI(*MBB, MI, DL, TII->get(TargetOpcode::COPY), RegA)
.addReg(MI->getOperand(0).getReg());
// Do the probe.
STI->getFrameLowering()->emitStackProbe(*MBB->getParent(), *MBB, MI, DL,
/*InPrologue=*/false);
break;
}
unsigned AmountReg = MI->getOperand(0).getReg();
MI->eraseFromParent();
// Delete the definition of AmountReg, possibly walking a chain of copies.
for (;;) {
if (!MRI->use_empty(AmountReg))
break;
MachineInstr *AmountDef = MRI->getUniqueVRegDef(AmountReg);
if (!AmountDef)
break;
if (AmountDef->isCopy() && AmountDef->getOperand(1).isReg())
AmountReg = AmountDef->getOperand(1).isReg();
AmountDef->eraseFromParent();
break;
}
}
bool X86WinAllocaExpander::runOnMachineFunction(MachineFunction &MF) {
if (!MF.getInfo<X86MachineFunctionInfo>()->hasWinAlloca())
return false;
MRI = &MF.getRegInfo();
STI = &MF.getSubtarget<X86Subtarget>();
TII = STI->getInstrInfo();
TRI = STI->getRegisterInfo();
StackPtr = TRI->getStackRegister();
SlotSize = TRI->getSlotSize();
StackProbeSize = 4096;
if (MF.getFunction()->hasFnAttribute("stack-probe-size")) {
MF.getFunction()
->getFnAttribute("stack-probe-size")
.getValueAsString()
.getAsInteger(0, StackProbeSize);
}
LoweringMap Lowerings;
computeLowerings(MF, Lowerings);
for (auto &P : Lowerings)
lower(P.first, P.second);
return true;
}

4
test/CodeGen/X86/cleanuppad-inalloca.ll
View File

@ -38,8 +38,8 @@ ehcleanup: ; preds = %entry
; CHECK: pushl %ebp
; CHECK: movl %esp, %ebp
; CHECK: subl ${{[0-9]+}}, %esp
; CHECK: movl $8, %eax
; CHECK: calll __chkstk
; CHECK: pushl %eax
; CHECK: pushl %eax
; CHECK: calll "??0A@@QAE@XZ"
; CHECK: calll "??0A@@QAE@XZ"
; CHECK: calll _takes_two

2
test/CodeGen/X86/dynamic-alloca-in-entry.ll
View File

@ -15,5 +15,5 @@ define void @bar() {
ret void
}
; CHECK-LABEL: _bar:
; CHECK: calll __chkstk
; CHECK: pushl %eax
; CHECK: retl

4
test/CodeGen/X86/inalloca-ctor.ll
View File

@ -12,8 +12,8 @@ define void @g() {
entry:
%args = alloca inalloca %frame
%c = getelementptr %frame, %frame* %args, i32 0, i32 2
; CHECK: movl $20, %eax
; CHECK: calll __chkstk
; CHECK: pushl %eax
; CHECK: subl $16, %esp
; CHECK: movl %esp,
call void @Foo_ctor(%Foo* %c)
; CHECK: leal 12(%{{.*}}),

3
test/CodeGen/X86/inalloca-invoke.ll
View File

@ -21,7 +21,8 @@ blah:
%beg = getelementptr %frame.reverse, %frame.reverse* %rev_args, i32 0, i32 0
%end = getelementptr %frame.reverse, %frame.reverse* %rev_args, i32 0, i32 1
; CHECK: calll __chkstk
; CHECK: pushl %eax
; CHECK: subl $20, %esp
; CHECK: movl %esp, %[[beg:[^ ]*]]
; CHECK: leal 12(%[[beg]]), %[[end:[^ ]*]]

4
test/CodeGen/X86/inalloca-stdcall.ll
View File

@ -8,8 +8,8 @@ declare x86_stdcallcc void @i(i32 %a)
define void @g() {
; CHECK-LABEL: _g:
%b = alloca inalloca %Foo
; CHECK: movl $8, %eax
; CHECK: calll __chkstk
; CHECK: pushl %eax
; CHECK: pushl %eax
%f1 = getelementptr %Foo, %Foo* %b, i32 0, i32 0
%f2 = getelementptr %Foo, %Foo* %b, i32 0, i32 1
store i32 13, i32* %f1

12
test/CodeGen/X86/inalloca.ll
View File

@ -8,8 +8,8 @@ define void @a() {
; CHECK-LABEL: _a:
entry:
%b = alloca inalloca %Foo
; CHECK: movl $8, %eax
; CHECK: calll __chkstk
; CHECK: pushl %eax
; CHECK: pushl %eax
%f1 = getelementptr %Foo, %Foo* %b, i32 0, i32 0
%f2 = getelementptr %Foo, %Foo* %b, i32 0, i32 1
store i32 13, i32* %f1
@ -28,8 +28,8 @@ define void @b() {
; CHECK-LABEL: _b:
entry:
%b = alloca inalloca %Foo
; CHECK: movl $8, %eax
; CHECK: calll __chkstk
; CHECK: pushl %eax
; CHECK: pushl %eax
%f1 = getelementptr %Foo, %Foo* %b, i32 0, i32 0
%f2 = getelementptr %Foo, %Foo* %b, i32 0, i32 1
store i32 13, i32* %f1
@ -49,8 +49,8 @@ define void @c() {
; CHECK-LABEL: _c:
entry:
%b = alloca inalloca %Foo
; CHECK: movl $8, %eax
; CHECK: calll __chkstk
; CHECK: pushl %eax
; CHECK: pushl %eax
%f1 = getelementptr %Foo, %Foo* %b, i32 0, i32 0
%f2 = getelementptr %Foo, %Foo* %b, i32 0, i32 1
store i32 13, i32* %f1

4
test/CodeGen/X86/shrink-wrap-chkstk.ll
View File

@ -7,7 +7,7 @@
target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
target triple = "i686-pc-windows-msvc18.0.0"
%struct.S = type { [12 x i8] }
%struct.S = type { [8192 x i8] }
define x86_thiscallcc void @call_inalloca(i1 %x) {
entry:
@ -29,7 +29,7 @@ bb2:
; CHECK-LABEL: _call_inalloca: # @call_inalloca
; CHECK: pushl %ebp
; CHECK: movl %esp, %ebp
; CHECK: movl $12, %eax
; CHECK: movl $8192, %eax
; CHECK: calll __chkstk
; CHECK: calll _inalloca_params
; CHECK: movl %ebp, %esp

153
test/CodeGen/X86/win-alloca-expander.ll Normal file
View File

@ -0,0 +1,153 @@
; RUN: llc < %s -mtriple=i686-pc-win32 | FileCheck %s
%struct.S = type { [1024 x i8] }
%struct.T = type { [3000 x i8] }
%struct.U = type { [10000 x i8] }
define void @basics() {
; CHECK-LABEL: basics:
entry:
br label %bb1
; Allocation move sizes should have been removed.
; CHECK-NOT: movl $1024
; CHECK-NOT: movl $3000
bb1:
%p0 = alloca %struct.S
; The allocation is small enough not to require stack probing, but the %esp
; offset after the prologue is not known, so the stack must be touched before
; the pointer is adjusted.
; CHECK: pushl %eax
; CHECK: subl $1020, %esp
%saved_stack = tail call i8* @llvm.stacksave()
%p1 = alloca %struct.S
; We know the %esp offset from above, so there is no need to touch the stack
; before adjusting it.
; CHECK: subl $1024, %esp
%p2 = alloca %struct.T
; The offset is now 2048 bytes, so allocating a T must touch the stack again.
; CHECK: pushl %eax
; CHECK: subl $2996, %esp
call void @f(%struct.S* %p0)
; CHECK: calll
%p3 = alloca %struct.T
; The call above touched the stack, so there is room for a T object.
; CHECK: subl $3000, %esp
%p4 = alloca %struct.U
; The U object is large enough to require stack probing.
; CHECK: movl $10000, %eax
; CHECK: calll __chkstk
%p5 = alloca %struct.T
; The stack probing above touched the tip of the stack, so there's room for a T.
; CHECK: subl $3000, %esp
call void @llvm.stackrestore(i8* %saved_stack)
%p6 = alloca %struct.S
; The stack restore means we lose track of the stack pointer and must probe.
; CHECK: pushl %eax
; CHECK: subl $1020, %esp
; Use the pointers so they're not optimized away.
call void @f(%struct.S* %p1)
call void @g(%struct.T* %p2)
call void @g(%struct.T* %p3)
call void @h(%struct.U* %p4)
call void @g(%struct.T* %p5)
ret void
}
define void @loop() {
; CHECK-LABEL: loop:
entry:
br label %bb1
bb1:
%p1 = alloca %struct.S
; The entry offset is unknown; touch-and-sub.
; CHECK: pushl %eax
; CHECK: subl $1020, %esp
br label %loop1
loop1:
%i1 = phi i32 [ 10, %bb1 ], [ %dec1, %loop1 ]
%p2 = alloca %struct.S
; We know the incoming offset from bb1, but from the back-edge, we assume the
; worst, and therefore touch-and-sub to allocate.
; CHECK: pushl %eax
; CHECK: subl $1020, %esp
%dec1 = sub i32 %i1, 1
%cmp1 = icmp sgt i32 %i1, 0
br i1 %cmp1, label %loop1, label %end
; CHECK: decl
; CHECK: jg
end:
call void @f(%struct.S* %p1)
call void @f(%struct.S* %p2)
ret void
}
define void @probe_size_attribute() "stack-probe-size"="512" {
; CHECK-LABEL: probe_size_attribute:
entry:
br label %bb1
bb1:
%p0 = alloca %struct.S
; The allocation would be small enough not to require probing, if it wasn't
; for the stack-probe-size attribute.
; CHECK: movl $1024, %eax
; CHECK: calll __chkstk
call void @f(%struct.S* %p0)
ret void
}
define void @cfg(i1 %x, i1 %y) {
; Test that the blocks are analyzed in the correct order.
; CHECK-LABEL: cfg:
entry:
br i1 %x, label %bb1, label %bb2
bb1:
%p1 = alloca %struct.S
; CHECK: pushl %eax
; CHECK: subl $1020, %esp
br label %bb3
bb2:
%p2 = alloca %struct.T
; CHECK: pushl %eax
; CHECK: subl $2996, %esp
br label %bb3
bb3:
br i1 %y, label %bb4, label %bb5
bb4:
%p4 = alloca %struct.S
; CHECK: subl $1024, %esp
call void @f(%struct.S* %p4)
ret void
bb5:
%p5 = alloca %struct.T
; CHECK: pushl %eax
; CHECK: subl $2996, %esp
call void @g(%struct.T* %p5)
ret void
}
declare void @f(%struct.S*)
declare void @g(%struct.T*)
declare void @h(%struct.U*)
declare i8* @llvm.stacksave()
declare void @llvm.stackrestore(i8*)