[X86] -fpatchable-function-entry=N,0: place patch label after ENDBR{32,64}

Similar to D73680 (AArch64 BTI).

A local linkage function whose address is not taken does not need ENDBR32/ENDBR64. Placing the patch label after ENDBR32/ENDBR64 has the advantage that code does not need to differentiate whether the function has an initial ENDBR.

Also, add 32-bit tests and test that .cfi_startproc is at the function
entry. The line information has a general implementation and is tested
by AArch64/patchable-function-entry-empty.mir

Reviewed By: nickdesaulniers

Differential Revision: https://reviews.llvm.org/D73760

(cherry picked from commit 8ff86fcf4c038c7156ed4f01e7ed35cae49489e2)

1 files changed, 19 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index 2fc9a2af01d..7f49c6e861d 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -2002,6 +2002,25 @@ void X86AsmPrinter::EmitInstruction(const MachineInstr *MI) {
     break;
   }
 
+  case X86::ENDBR32:
+  case X86::ENDBR64: {
+    // CurrentPatchableFunctionEntrySym can be CurrentFnBegin only for
+    // -fpatchable-function-entry=N,0. The entry MBB is guaranteed to be
+    // non-empty. If MI is the initial ENDBR, place the
+    // __patchable_function_entries label after ENDBR.
+    if (CurrentPatchableFunctionEntrySym &&
+        CurrentPatchableFunctionEntrySym == CurrentFnBegin &&
+        MI == &MF->front().front()) {
+      MCInst Inst;
+      MCInstLowering.Lower(MI, Inst);
+      EmitAndCountInstruction(Inst);
+      CurrentPatchableFunctionEntrySym = createTempSymbol("patch");
+      OutStreamer->EmitLabel(CurrentPatchableFunctionEntrySym);
+      return;
+    }
+    break;
+  }
+
   case X86::TAILJMPr:
   case X86::TAILJMPm:
   case X86::TAILJMPd: