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[WebAssembly] Refine block placement to insert blocks between trees. 

Refine the test for whether an instruction is in an expression tree so that
it detects when one tree ends and another begins, so we can place a block
at that point, rather than continuing to find the first instruction not in
a tree at all.

llvm-svn: 259294
This commit is contained in:
Dan Gohman 2016-01-30 05:01:06 +00:00
parent 43976df0da
commit ed0f113885
2 changed files with 26 additions and 9 deletions
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27
llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
View File

@ -27,6 +27,7 @@
#include "WebAssembly.h"
#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "WebAssemblyMachineFunctionInfo.h"
#include "WebAssemblySubtarget.h"
#include "llvm/ADT/SCCIterator.h"
#include "llvm/ADT/SetVector.h"
@ -266,12 +267,26 @@ static bool ExplicitlyBranchesTo(MachineBasicBlock *Pred,
return false;
}
/// Test whether MI is a child of some other node in an expression tree.
static bool IsChild(const MachineInstr *MI,
const WebAssemblyFunctionInfo &MFI) {
if (MI->getNumOperands() == 0)
return false;
const MachineOperand &MO = MI->getOperand(0);
if (!MO.isReg() || MO.isImplicit() || !MO.isDef())
return false;
unsigned Reg = MO.getReg();
return TargetRegisterInfo::isVirtualRegister(Reg) &&
MFI.isVRegStackified(Reg);
}
/// Insert a BLOCK marker for branches to MBB (if needed).
static void PlaceBlockMarker(MachineBasicBlock &MBB, MachineFunction &MF,
SmallVectorImpl<MachineBasicBlock *> &ScopeTops,
const WebAssemblyInstrInfo &TII,
const MachineLoopInfo &MLI,
MachineDominatorTree &MDT) {
MachineDominatorTree &MDT,
WebAssemblyFunctionInfo &MFI) {
// First compute the nearest common dominator of all forward non-fallthrough
// predecessors so that we minimize the time that the BLOCK is on the stack,
// which reduces overall stack height.
@ -326,7 +341,7 @@ static void PlaceBlockMarker(MachineBasicBlock &MBB, MachineFunction &MF,
// beginning of the local expression tree and any nested BLOCKs.
InsertPos = Header->getFirstTerminator();
while (InsertPos != Header->begin() &&
prev(InsertPos)->definesRegister(WebAssembly::EXPR_STACK) &&
IsChild(prev(InsertPos), MFI) &&
prev(InsertPos)->getOpcode() != WebAssembly::LOOP &&
prev(InsertPos)->getOpcode() != WebAssembly::END_BLOCK &&
prev(InsertPos)->getOpcode() != WebAssembly::END_LOOP)
@ -409,7 +424,8 @@ GetDepth(const SmallVectorImpl<const MachineBasicBlock *> &Stack,
/// Insert LOOP and BLOCK markers at appropriate places.
static void PlaceMarkers(MachineFunction &MF, const MachineLoopInfo &MLI,
const WebAssemblyInstrInfo &TII,
MachineDominatorTree &MDT) {
MachineDominatorTree &MDT,
WebAssemblyFunctionInfo &MFI) {
// For each block whose label represents the end of a scope, record the block
// which holds the beginning of the scope. This will allow us to quickly skip
// over scoped regions when walking blocks. We allocate one more than the
@ -425,7 +441,7 @@ static void PlaceMarkers(MachineFunction &MF, const MachineLoopInfo &MLI,
PlaceLoopMarker(MBB, MF, ScopeTops, LoopTops, TII, MLI);
// Place the BLOCK for MBB if MBB is branched to from above.
PlaceBlockMarker(MBB, MF, ScopeTops, TII, MLI, MDT);
PlaceBlockMarker(MBB, MF, ScopeTops, TII, MLI, MDT, MFI);
}
// Now rewrite references to basic blocks to be depth immediates.
@ -478,6 +494,7 @@ bool WebAssemblyCFGStackify::runOnMachineFunction(MachineFunction &MF) {
auto &MDT = getAnalysis<MachineDominatorTree>();
// Liveness is not tracked for EXPR_STACK physreg.
const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
WebAssemblyFunctionInfo &MFI = *MF.getInfo<WebAssemblyFunctionInfo>();
MF.getRegInfo().invalidateLiveness();
// RPO sorting needs all loops to be single-entry.
@ -487,7 +504,7 @@ bool WebAssemblyCFGStackify::runOnMachineFunction(MachineFunction &MF) {
SortBlocks(MF, MLI);
// Place the BLOCK and LOOP markers to indicate the beginnings of scopes.
PlaceMarkers(MF, MLI, TII, MDT);
PlaceMarkers(MF, MLI, TII, MDT, MFI);
return true;
}

8
llvm/test/CodeGen/WebAssembly/cfg-stackify.ll
View File

@ -949,9 +949,9 @@ bb6:
; CHECK-NEXT: block{{$}}
; CHECK-NEXT: block{{$}}
; CHECK: br_if {{[^,]+}}, 0{{$}}
; CHECK-NEXT: block{{$}}
; CHECK-NOT: block
; CHECK: br_if {{[^,]+}}, 0{{$}}
; CHECK: block{{$}}
; CHECK-NEXT: br_if {{[^,]+}}, 0{{$}}
; CHECK-NOT: block
; CHECK: br_if {{[^,]+}}, 2{{$}}
; CHECK-NEXT: .LBB20_3:
@ -980,9 +980,9 @@ bb6:
; OPT: block{{$}}
; OPT-NEXT: block{{$}}
; OPT: br_if $pop{{[0-9]+}}, 0{{$}}
; OPT-NEXT: block{{$}}
; OPT-NOT: block
; OPT: br_if $0, 0{{$}}
; OPT: block{{$}}
; OPT-NEXT: br_if $0, 0{{$}}
; OPT-NOT: block
; OPT: br_if {{[^,]+}}, 2{{$}}
; OPT-NEXT: .LBB20_3: