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[WebAssembly] Convert stackified IMPLICIT_DEF into constant 0. 

Since IMPLIFIT_DEF instructions are omitted in the output, when the output
of an IMPLICIT_DEF instruction is stackified, the resulting register lacks
an explicit push, leading to a push/pop mismatch. Fix this by converting
such IMPLICIT_DEFs into CONST_I32 0 instructions so that they have explicit
pushes.

llvm-svn: 286274
This commit is contained in:
Dan Gohman 2016-11-08 19:40:38 +00:00
parent 53a03a28c4
commit e81021a5cb
2 changed files with 87 additions and 0 deletions
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37
llvm/lib/Target/WebAssembly/WebAssemblyRegStackify.cpp
View File

@ -87,6 +87,37 @@ static void ImposeStackOrdering(MachineInstr *MI) {
/*isImp=*/true));
}
// Convert an IMPLICIT_DEF instruction into an instruction which defines
// a constant zero value.
static void ConvertImplicitDefToConstZero(MachineInstr *MI,
MachineRegisterInfo &MRI,
const TargetInstrInfo *TII,
MachineFunction &MF) {
assert(MI->getOpcode() == TargetOpcode::IMPLICIT_DEF);
const auto *RegClass =
MRI.getRegClass(MI->getOperand(0).getReg());
if (RegClass == &WebAssembly::I32RegClass) {
MI->setDesc(TII->get(WebAssembly::CONST_I32));
MI->addOperand(MachineOperand::CreateImm(0));
} else if (RegClass == &WebAssembly::I64RegClass) {
MI->setDesc(TII->get(WebAssembly::CONST_I64));
MI->addOperand(MachineOperand::CreateImm(0));
} else if (RegClass == &WebAssembly::F32RegClass) {
MI->setDesc(TII->get(WebAssembly::CONST_F32));
ConstantFP *Val = cast<ConstantFP>(Constant::getNullValue(
Type::getFloatTy(MF.getFunction()->getContext())));
MI->addOperand(MachineOperand::CreateFPImm(Val));
} else if (RegClass == &WebAssembly::F64RegClass) {
MI->setDesc(TII->get(WebAssembly::CONST_F64));
ConstantFP *Val = cast<ConstantFP>(Constant::getNullValue(
Type::getDoubleTy(MF.getFunction()->getContext())));
MI->addOperand(MachineOperand::CreateFPImm(Val));
} else {
llvm_unreachable("Unexpected reg class");
}
}
// Determine whether a call to the callee referenced by
// MI->getOperand(CalleeOpNo) reads memory, writes memory, and/or has side
// effects.
@ -791,6 +822,12 @@ bool WebAssemblyRegStackify::runOnMachineFunction(MachineFunction &MF) {
continue;
}
// If the instruction we just stackified is an IMPLICIT_DEF, convert it
// to a constant 0 so that the def is explicit, and the push/pop
// correspondence is maintained.
if (Insert->getOpcode() == TargetOpcode::IMPLICIT_DEF)
ConvertImplicitDefToConstZero(Insert, MRI, TII, MF);
// We stackified an operand. Add the defining instruction's operands to
// the worklist stack now to continue to build an ever deeper tree.
Commuting.Reset();

50
llvm/test/CodeGen/WebAssembly/implicit-def.ll Normal file
View File

@ -0,0 +1,50 @@
; RUN: llc -o - %s | FileCheck %s
target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
target triple = "wasm32-unknown-unknown"
; Test that stackified IMPLICIT_DEF instructions are converted into
; CONST_I32 to provide an explicit push.
; CHECK: br_if 2,
; CHECK: i32.const $push[[L0:[0-9]+]]=, 0{{$}}
; CHECK-NEXT: return $pop[[L0]]{{$}}
define i1 @f() {
%a = xor i1 0, 0
switch i1 %a, label %C [
i1 0, label %A
i1 1, label %B
]
A:
%b = xor i1 0, 0
br label %X
B:
%c = xor i1 0, 0
br i1 %c, label %D, label %X
C:
%d = icmp slt i32 0, 0
br i1 %d, label %G, label %F
D:
%e = xor i1 0, 0
br i1 %e, label %E, label %X
E:
%f = xor i1 0, 0
br label %X
F:
%g = xor i1 0, 0
br label %G
G:
%h = phi i1 [ undef, %C ], [ false, %F ]
br label %X
X:
%i = phi i1 [ true, %A ], [ true, %B ], [ true, %D ], [ true, %E ], [ %h, %G ]
ret i1 %i
}