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Stackmap shadows should consider call returns a branch target.

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To avoid emitting too many nops, a stackmap shadow can include emitted instructions in the shadow, but these must not include branch targets.

A return from a call should count as a branch target as patching over the instructions after the call would lead to incorrect behaviour for threads currently making that call, when they return.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220710 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Pete Cooper 2014-10-27 19:40:35 +00:00
parent b11c5b1078
commit 7476f9c513
2 changed files with 12 additions and 4 deletions
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6
lib/Target/X86/X86MCInstLower.cpp
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@ -1210,4 +1210,10 @@ void X86AsmPrinter::EmitInstruction(const MachineInstr *MI) {
MCInst TmpInst;
MCInstLowering.Lower(MI, TmpInst);
EmitAndCountInstruction(TmpInst);
// Stackmap shadows cannot include branch targets, so we can count the bytes
// in a call towards the shadow, but must flush the shadow immediately after
// to account for the return from the call.
if (MI->isCall())
SMShadowTracker.emitShadowPadding(OutStreamer, getSubtargetInfo());
}

10
test/CodeGen/X86/stackmap-shadow-optimization.ll
View File

@ -1,16 +1,18 @@
; RUN: llc < %s -mtriple=x86_64-apple-darwin -mcpu=corei7 | FileCheck %s
; Check that the X86 stackmap shadow optimization is only outputting a 1-byte
; nop here. 8-bytes are requested, but 7 are covered by the code for the call to
; bar, the frame teardown and the return.
; Check that the X86 stackmap shadow optimization is only outputting a 3-byte
; nop here. 8-bytes are requested, but 5 are covered by the code for the call to
; bar. However, the frame teardown and the return do not count towards the
; stackmap shadow as the call return counts as a branch target so must flush
; the shadow.
define void @shadow_optimization_test() {
entry:
; CHECK-LABEL: shadow_optimization_test:
; CHECK: callq _bar
; CHECK-NOT: nop
; CHECK: callq _bar
; CHECK: retq
; CHECK: nop
; CHECK: retq
call void @bar()
tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 0, i32 8)
call void @bar()