[XRay] support conditional return on PPC.
Summary: Conditional returns were not taken into consideration at all. Implement them by turning them into jumps and normal returns. This means there is a slightly higher performance penalty for conditional returns, but this is the best we can do, and it still disturbs little of the rest.
Reviewers: dberris, echristo
Subscribers: sanjoy, nemanjai, hiraditya, kbarton, llvm-commits
Differential Revision: https://reviews.llvm.org/D38102
llvm-svn: 314005
diff --git a/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp b/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp
index 67c849b..7fee5ff 100644
--- a/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp
+++ b/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp
@@ -19,6 +19,7 @@
#include "InstPrinter/PPCInstPrinter.h"
#include "MCTargetDesc/PPCMCExpr.h"
#include "MCTargetDesc/PPCMCTargetDesc.h"
+#include "MCTargetDesc/PPCPredicates.h"
#include "PPC.h"
#include "PPCInstrInfo.h"
#include "PPCMachineFunctionInfo.h"
@@ -1089,7 +1090,61 @@
recordSled(BeginOfSled, *MI, SledKind::FUNCTION_ENTER);
break;
}
- case TargetOpcode::PATCHABLE_FUNCTION_EXIT: {
+ case TargetOpcode::PATCHABLE_RET: {
+ unsigned RetOpcode = MI->getOperand(0).getImm();
+ MCInst RetInst;
+ RetInst.setOpcode(RetOpcode);
+ for (const auto &MO :
+ make_range(std::next(MI->operands_begin()), MI->operands_end())) {
+ MCOperand MCOp;
+ if (LowerPPCMachineOperandToMCOperand(MO, MCOp, *this, false))
+ RetInst.addOperand(MCOp);
+ }
+
+ bool IsConditional;
+ if (RetOpcode == PPC::BCCLR) {
+ IsConditional = true;
+ } else if (RetOpcode == PPC::TCRETURNdi8 || RetOpcode == PPC::TCRETURNri8 ||
+ RetOpcode == PPC::TCRETURNai8) {
+ break;
+ } else if (RetOpcode == PPC::BLR8 || RetOpcode == PPC::TAILB8) {
+ IsConditional = false;
+ } else {
+ EmitToStreamer(*OutStreamer, RetInst);
+ break;
+ }
+
+ MCSymbol *FallthroughLabel;
+ if (IsConditional) {
+ // Before:
+ // bgtlr cr0
+ //
+ // After:
+ // ble cr0, .end
+ // .p2align 3
+ // .begin:
+ // blr # lis 0, FuncId[16..32]
+ // nop # li 0, FuncId[0..15]
+ // std 0, -8(1)
+ // mflr 0
+ // bl __xray_FunctionExit
+ // mtlr 0
+ // blr
+ // .end:
+ //
+ // Update compiler-rt/lib/xray/xray_powerpc64.cc accordingly when number
+ // of instructions change.
+ FallthroughLabel = OutContext.createTempSymbol();
+ EmitToStreamer(
+ *OutStreamer,
+ MCInstBuilder(PPC::BCC)
+ .addImm(PPC::InvertPredicate(
+ static_cast<PPC::Predicate>(MI->getOperand(1).getImm())))
+ .addReg(MI->getOperand(2).getReg())
+ .addExpr(MCSymbolRefExpr::create(FallthroughLabel, OutContext)));
+ RetInst = MCInst();
+ RetInst.setOpcode(PPC::BLR8);
+ }
// .p2align 3
// .begin:
// b(lr)? # lis 0, FuncId[16..32]
@@ -1098,24 +1153,14 @@
// mflr 0
// bl __xray_FunctionExit
// mtlr 0
- // .end:
// b(lr)?
//
// Update compiler-rt/lib/xray/xray_powerpc64.cc accordingly when number
// of instructions change.
- const MachineInstr *Next = [&] {
- MachineBasicBlock::const_iterator It(MI);
- assert(It != MI->getParent()->end());
- ++It;
- assert(It->isReturn());
- return &*It;
- }();
OutStreamer->EmitCodeAlignment(8);
MCSymbol *BeginOfSled = OutContext.createTempSymbol();
OutStreamer->EmitLabel(BeginOfSled);
- MCInst TmpInst;
- LowerPPCMachineInstrToMCInst(Next, TmpInst, *this, false);
- EmitToStreamer(*OutStreamer, TmpInst);
+ EmitToStreamer(*OutStreamer, RetInst);
EmitToStreamer(*OutStreamer, MCInstBuilder(PPC::NOP));
EmitToStreamer(
*OutStreamer,
@@ -1127,17 +1172,18 @@
OutContext.getOrCreateSymbol("__xray_FunctionExit"),
OutContext)));
EmitToStreamer(*OutStreamer, MCInstBuilder(PPC::MTLR8).addReg(PPC::X0));
+ EmitToStreamer(*OutStreamer, RetInst);
+ if (IsConditional)
+ OutStreamer->EmitLabel(FallthroughLabel);
recordSled(BeginOfSled, *MI, SledKind::FUNCTION_EXIT);
break;
}
+ case TargetOpcode::PATCHABLE_FUNCTION_EXIT:
+ llvm_unreachable("PATCHABLE_FUNCTION_EXIT should never be emitted");
case TargetOpcode::PATCHABLE_TAIL_CALL:
// TODO: Define a trampoline `__xray_FunctionTailExit` and differentiate a
// normal function exit from a tail exit.
- case TargetOpcode::PATCHABLE_RET:
- // PPC's tail call instruction, e.g. PPC::TCRETURNdi8, doesn't really
- // lower to a PPC::B instruction. The PPC::B instruction is generated
- // before it, and handled by the normal case.
- llvm_unreachable("Tail call is handled in the normal case. See comments"
+ llvm_unreachable("Tail call is handled in the normal case. See comments "
"around this assert.");
}
}