[XRay][CodeGen][PowerPC] Fix tail exit codegen for XRay in PPC

Summary:
This fixes code-gen for XRay in PPC. The regression wasn't caught by
codegen tests  which we add in this change.

What happened was the following:

- For tail exits, we used to unconditionally prepend the returns/exits
  with a pseudo-instruction that gets lowered to the instrumentation
  sled (and leave the actual return/exit instruction as-is).
- Changes to the XRay instrumentation pass caused the tail exits to
  suddenly also emit the tail exit pseudo-instruction, since the check
  for whether a return instruction was also a call instruction meant it
  was a tail exit instruction.
- None of the tests caught the regression either due to non-existent
  tests, or the tests being disabled/removed for continuous breakage.

This change re-introduces some of the basic tests and verifies that
we're back to a state that allows the back-end to generate appropriate
XRay instrumented binaries for PPC in the presence of tail exits.

Reviewers: echristo, timshen

Subscribers: nemanjai, kbarton, llvm-commits

Differential Revision: https://reviews.llvm.org/D37570

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@312772 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/XRayInstrumentation.cpp

@@ -14,8 +14,8 @@
 //
 //===---------------------------------------------------------------------===//
 
-#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineDominators.h"
@@ -109,22 +109,13 @@ void XRayInstrumentation::replaceRetWithPatchableRet(
 
 void XRayInstrumentation::prependRetWithPatchableExit(
     MachineFunction &MF, const TargetInstrInfo *TII) {
-  for (auto &MBB : MF) {
-    for (auto &T : MBB.terminators()) {
-      unsigned Opc = 0;
+  for (auto &MBB : MF)
+    for (auto &T : MBB.terminators())
       if (T.isReturn()) {
-        Opc = TargetOpcode::PATCHABLE_FUNCTION_EXIT;
-      }
-      if (TII->isTailCall(T)) {
-        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));
+        // Prepend the return instruction with PATCHABLE_FUNCTION_EXIT.
+        BuildMI(MBB, T, T.getDebugLoc(),
+                TII->get(TargetOpcode::PATCHABLE_FUNCTION_EXIT));
       }
-    }
-  }
 }
 
 bool XRayInstrumentation::runOnMachineFunction(MachineFunction &MF) {
@@ -143,7 +134,7 @@ bool XRayInstrumentation::runOnMachineFunction(MachineFunction &MF) {
 
     // Count the number of MachineInstr`s in MachineFunction
     int64_t MICount = 0;
-    for (const auto& MBB : MF)
+    for (const auto &MBB : MF)
       MICount += MBB.size();
 
     // Check if we have a loop.

lib/Target/PowerPC/PPCAsmPrinter.cpp

@@ -1131,6 +1131,8 @@ void PPCLinuxAsmPrinter::EmitInstruction(const MachineInstr *MI) {
     break;
   }
   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

test/CodeGen/PowerPC/xray-attribute-instrumentation.ll

@@ -0,0 +1,44 @@
+; RUN: llc -filetype=asm -o - -mtriple=powerpc64le-unknown-linux-gnu < %s | FileCheck %s
+; RUN: llc -filetype=asm -o - -mtriple=powerpc64le-unknown-linux-gnu \
+; RUN:    -relocation-model=pic < %s | FileCheck %s
+
+define i32 @foo() nounwind noinline uwtable "function-instrument"="xray-always" {
+; CHECK-LABEL: .Ltmp0:
+; CHECK:              b .Ltmp1
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         std 0, -8(1)
+; CHECK-NEXT:         mflr 0
+; CHECK-NEXT:         bl __xray_FunctionEntry
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         mtlr 0
+; CHECK-LABEL: .Ltmp1:
+  ret i32 0
+; CHECK-LABEL: .Ltmp2:
+; CHECK:              blr
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         std 0, -8(1)
+; CHECK-NEXT:         mflr 0
+; CHECK-NEXT:         bl __xray_FunctionExit
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         mtlr 0
+}
+; CHECK-LABEL: xray_instr_map,"awo",@progbits,.text,unique,1
+; CHECK:      .Lxray_sleds_start0:
+; CHECK-NEXT:         .quad   .Ltmp0
+; CHECK-NEXT:         .quad   foo
+; CHECK-NEXT:         .byte   0x00
+; CHECK-NEXT:         .byte   0x01
+; CHECK-NEXT:         .byte   0x00
+; CHECK-NEXT:         .space  13
+; CHECK-NEXT:         .quad   .Ltmp2
+; CHECK-NEXT:         .quad   foo
+; CHECK-NEXT:         .byte   0x01
+; CHECK-NEXT:         .byte   0x01
+; CHECK-NEXT:         .byte   0x00
+; CHECK-NEXT:         .space  13
+; CHECK-NEXT: .Lxray_sleds_end0:
+; CHECK-LABEL: xray_fn_idx,"awo",@progbits,.text,unique,1
+; CHECK:              .p2align        4
+; CHECK-NEXT:         .quad   .Lxray_sleds_start0
+; CHECK-NEXT:         .quad   .Lxray_sleds_end0
+; CHECK-NEXT:         .text

test/CodeGen/PowerPC/xray-tail-call-hidden.ll

@@ -0,0 +1,26 @@
+; RUN: llc -filetype=asm -o - -mtriple=powerpc64le-unknown-linux-gnu < %s | FileCheck %s
+
+declare hidden i32 @callee() nounwind noinline uwtable "function-instrument"="xray-always"
+
+define i32 @caller() nounwind noinline uwtable "function-instrument"="xray-always" {
+; CHECK-LABEL: .Ltmp0:
+; CHECK:              b .Ltmp1
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         std 0, -8(1)
+; CHECK-NEXT:         mflr 0
+; CHECK-NEXT:         bl __xray_FunctionEntry
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         mtlr 0
+; CHECK-LABEL: .Ltmp1:
+  %retval = tail call i32 @callee()
+  ret i32 %retval
+; CHECK-LABEL: .Ltmp2:
+; CHECK:              b callee
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         std 0, -8(1)
+; CHECK-NEXT:         mflr 0
+; CHECK-NEXT:         bl __xray_FunctionExit
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         mtlr 0
+}
+

test/CodeGen/PowerPC/xray-tail-call-sled.ll

@@ -0,0 +1,44 @@
+; RUN: llc -filetype=asm -o - -mtriple=powerpc64le-unknown-linux-gnu < %s | FileCheck %s
+
+define i32 @callee() nounwind noinline uwtable "function-instrument"="xray-always" {
+; CHECK-LABEL: .Ltmp0:
+; CHECK:              b .Ltmp1
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         std 0, -8(1)
+; CHECK-NEXT:         mflr 0
+; CHECK-NEXT:         bl __xray_FunctionEntry
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         mtlr 0
+; CHECK-LABEL: .Ltmp1:
+  ret i32 0
+; CHECK-LABEL: .Ltmp2:
+; CHECK:              blr
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         std 0, -8(1)
+; CHECK-NEXT:         mflr 0
+; CHECK-NEXT:         bl __xray_FunctionExit
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         mtlr 0
+}
+
+define i32 @caller() nounwind noinline uwtable "function-instrument"="xray-always" {
+; CHECK-LABEL: .Ltmp3:
+; CHECK:              b .Ltmp4
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         std 0, -8(1)
+; CHECK-NEXT:         mflr 0
+; CHECK-NEXT:         bl __xray_FunctionEntry
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         mtlr 0
+; CHECK-LABEL: .Ltmp4:
+  %retval = tail call i32 @callee()
+  ret i32 %retval
+; CHECK-LABEL: .Ltmp5:
+; CHECK:              blr
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         std 0, -8(1)
+; CHECK-NEXT:         mflr 0
+; CHECK-NEXT:         bl __xray_FunctionExit
+; CHECK-NEXT:         nop
+; CHECK-NEXT:         mtlr 0
+}