[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/CodeGen/XRayInstrumentation.cpp b/llvm/lib/CodeGen/XRayInstrumentation.cpp
index e6b6582..2063ab1 100644
--- a/llvm/lib/CodeGen/XRayInstrumentation.cpp
+++ b/llvm/lib/CodeGen/XRayInstrumentation.cpp
@@ -34,6 +34,15 @@
namespace {
+struct InstrumentationOptions {
+ // Whether to emit PATCHABLE_TAIL_CALL.
+ bool HandleTailcall;
+
+ // Whether to emit PATCHABLE_RET/PATCHABLE_FUNCTION_EXIT for all forms of
+ // return, e.g. conditional return.
+ bool HandleAllReturns;
+};
+
struct XRayInstrumentation : public MachineFunctionPass {
static char ID;
@@ -59,7 +68,8 @@
// This is the approach to go on CPUs which have a single RET instruction,
// like x86/x86_64.
void replaceRetWithPatchableRet(MachineFunction &MF,
- const TargetInstrInfo *TII);
+ const TargetInstrInfo *TII,
+ InstrumentationOptions);
// Prepend the original return instruction with the exit sled code ("patchable
// function exit" pseudo-instruction), preserving the original return
@@ -70,25 +80,28 @@
// have to call the trampoline and return from it to the original return
// instruction of the function being instrumented.
void prependRetWithPatchableExit(MachineFunction &MF,
- const TargetInstrInfo *TII);
+ const TargetInstrInfo *TII,
+ InstrumentationOptions);
};
} // end anonymous namespace
void XRayInstrumentation::replaceRetWithPatchableRet(
- MachineFunction &MF, const TargetInstrInfo *TII) {
+ MachineFunction &MF, const TargetInstrInfo *TII,
+ InstrumentationOptions op) {
// We look for *all* terminators and returns, then replace those with
// PATCHABLE_RET instructions.
SmallVector<MachineInstr *, 4> Terminators;
for (auto &MBB : MF) {
for (auto &T : MBB.terminators()) {
unsigned Opc = 0;
- if (T.isReturn() && T.getOpcode() == TII->getReturnOpcode()) {
+ if (T.isReturn() &&
+ (op.HandleAllReturns || T.getOpcode() == TII->getReturnOpcode())) {
// Replace return instructions with:
// PATCHABLE_RET <Opcode>, <Operand>...
Opc = TargetOpcode::PATCHABLE_RET;
}
- if (TII->isTailCall(T)) {
+ if (TII->isTailCall(T) && op.HandleTailcall) {
// Treat the tail call as a return instruction, which has a
// different-looking sled than the normal return case.
Opc = TargetOpcode::PATCHABLE_TAIL_CALL;
@@ -108,14 +121,24 @@
}
void XRayInstrumentation::prependRetWithPatchableExit(
- MachineFunction &MF, const TargetInstrInfo *TII) {
+ MachineFunction &MF, const TargetInstrInfo *TII,
+ InstrumentationOptions op) {
for (auto &MBB : MF)
- for (auto &T : MBB.terminators())
- if (T.isReturn()) {
- // Prepend the return instruction with PATCHABLE_FUNCTION_EXIT.
- BuildMI(MBB, T, T.getDebugLoc(),
- TII->get(TargetOpcode::PATCHABLE_FUNCTION_EXIT));
+ for (auto &T : MBB.terminators()) {
+ unsigned Opc = 0;
+ if (T.isReturn() &&
+ (op.HandleAllReturns || T.getOpcode() == TII->getReturnOpcode())) {
+ Opc = TargetOpcode::PATCHABLE_FUNCTION_EXIT;
}
+ if (TII->isTailCall(T) && op.HandleTailcall) {
+ Opc = TargetOpcode::PATCHABLE_TAIL_CALL;
+ }
+ if (Opc != 0) {
+ // Prepend the return instruction with PATCHABLE_FUNCTION_EXIT or
+ // PATCHABLE_TAIL_CALL .
+ BuildMI(MBB, T, T.getDebugLoc(), TII->get(Opc));
+ }
+ }
}
bool XRayInstrumentation::runOnMachineFunction(MachineFunction &MF) {
@@ -171,20 +194,35 @@
case Triple::ArchType::arm:
case Triple::ArchType::thumb:
case Triple::ArchType::aarch64:
- case Triple::ArchType::ppc64le:
case Triple::ArchType::mips:
case Triple::ArchType::mipsel:
case Triple::ArchType::mips64:
- case Triple::ArchType::mips64el:
+ case Triple::ArchType::mips64el: {
// For the architectures which don't have a single return instruction
- prependRetWithPatchableExit(MF, TII);
+ InstrumentationOptions op;
+ op.HandleTailcall = false;
+ op.HandleAllReturns = true;
+ prependRetWithPatchableExit(MF, TII, op);
break;
- default:
+ }
+ case Triple::ArchType::ppc64le: {
+ // PPC has conditional returns. Turn them into branch and plain returns.
+ InstrumentationOptions op;
+ op.HandleTailcall = false;
+ op.HandleAllReturns = true;
+ replaceRetWithPatchableRet(MF, TII, op);
+ break;
+ }
+ default: {
// For the architectures that have a single return instruction (such as
// RETQ on x86_64).
- replaceRetWithPatchableRet(MF, TII);
+ InstrumentationOptions op;
+ op.HandleTailcall = true;
+ op.HandleAllReturns = false;
+ replaceRetWithPatchableRet(MF, TII, op);
break;
}
+ }
return true;
}