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[AArch64][Stackmaps] Optimize stackmap shadows on AArch64.

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Reduce the number of nops emitted for stackmap shadows on AArch64 by counting
non-stackmap instructions up to the next branch target towards the requested
shadow.

<rdar://problem/14959522>



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223156 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Lang Hames 2014-12-02 21:36:24 +00:00
parent d90fc9d0fc
commit 26cc5bea39
2 changed files with 31 additions and 1 deletions
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17
lib/Target/AArch64/AArch64AsmPrinter.cpp
View File

@ -381,8 +381,23 @@ void AArch64AsmPrinter::LowerSTACKMAP(MCStreamer &OutStreamer, StackMaps &SM,
unsigned NumNOPBytes = MI.getOperand(1).getImm();
SM.recordStackMap(MI);
// Emit padding.
assert(NumNOPBytes % 4 == 0 && "Invalid number of NOP bytes requested!");
// Scan ahead to trim the shadow.
const MachineBasicBlock &MBB = *MI.getParent();
MachineBasicBlock::const_iterator MII(MI);
++MII;
while (NumNOPBytes > 0) {
if (MII == MBB.end() || MII->isCall() ||
MII->getOpcode() == AArch64::DBG_VALUE ||
MII->getOpcode() == TargetOpcode::PATCHPOINT ||
MII->getOpcode() == TargetOpcode::STACKMAP)
break;
++MII;
NumNOPBytes -= 4;
}
// Emit nops.
for (unsigned i = 0; i < NumNOPBytes; i += 4)
EmitToStreamer(OutStreamer, MCInstBuilder(AArch64::HINT).addImm(0));
}

15
test/CodeGen/AArch64/arm64-stackmap-nops.ll Normal file
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@ -0,0 +1,15 @@
; RUN: llc < %s -mtriple=arm64-apple-darwin | FileCheck %s
define void @test_shadow_optimization() {
entry:
; Expect 8 bytes worth of nops here rather than 16: With the shadow optimization
; in place, 8 bytes will be consumed by the frame teardown and return instr.
; CHECK-LABEL: test_shadow_optimization:
; CHECK: nop
; CHECK-NEXT: nop
; CHECK-NOT: nop
tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 0, i32 16)
ret void
}
declare void @llvm.experimental.stackmap(i64, i32, ...)