[PATCH] D134915: [X86] Do not emit JCC to __x86_indirect_thunk

[Joao Moreira via Phabricator via llvm-commits]

joaomoreira updated this revision to Diff 464411.
joaomoreira marked 3 inline comments as done.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D134915/new/

https://reviews.llvm.org/D134915

Files:
  llvm/lib/Target/X86/X86InstrInfo.cpp
  llvm/test/CodeGen/X86/jcc-indirect-thunk-kernel.ll


Index: llvm/test/CodeGen/X86/jcc-indirect-thunk-kernel.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/X86/jcc-indirect-thunk-kernel.ll
@@ -0,0 +1,32 @@
+; RUN: llc < %s -O2 --code-model=kernel | FileCheck %s
+; The intent of the test is that we do not generate conditional
+; tail calls to the thunk.
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define dso_local void @foo(ptr %something) #0 {
+; CHECK-LABEL: foo:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    movq (%rdi), %r11
+; CHECK-NEXT:    testq %r11, %r11
+; Make sure that a JNE was not generated instead of a JE + JMP sequence
+; CHECK-NOT:     jne
+; CHECK-NEXT:    je .LBB0_1
+; CHECK-NEXT:    bb.2: # %if.then
+; CHECK-NEXT:    jmp __x86_indirect_thunk_r11
+; CHECK-NEXT:    LBB0_1:
+; CHECK-NEXT:    retq
+entry:
+  %0 = load ptr, ptr %something, align 8
+  %tobool.not = icmp eq ptr %0, null
+  br i1 %tobool.not, label %if.end, label %if.then
+
+if.then:
+  tail call void %0()
+  br label %if.end
+
+if.end:
+  ret void
+}
+
+attributes #0 = { optsize "target-features"="+retpoline-external-thunk" }
Index: llvm/lib/Target/X86/X86InstrInfo.cpp
===================================================================
--- llvm/lib/Target/X86/X86InstrInfo.cpp
+++ llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -2942,13 +2942,26 @@
 bool X86InstrInfo::canMakeTailCallConditional(
     SmallVectorImpl<MachineOperand> &BranchCond,
     const MachineInstr &TailCall) const {
+
+  const MachineFunction *MF = TailCall.getMF();
+
+  if (MF->getTarget().getCodeModel() == CodeModel::Kernel) {
+    // Kernel patches thunk calls in runtime, these should never be conditional.
+    const MachineOperand &Target = TailCall.getOperand(0);
+    if (Target.isSymbol()) {
+      StringRef Symbol(Target.getSymbolName());
+      // this is currently only relevant to r11/kernel indirect thunk.
+      if (Symbol.equals("__x86_indirect_thunk_r11"))
+        return false;
+    }
+  }
+
   if (TailCall.getOpcode() != X86::TCRETURNdi &&
       TailCall.getOpcode() != X86::TCRETURNdi64) {
     // Only direct calls can be done with a conditional branch.
     return false;
   }
 
-  const MachineFunction *MF = TailCall.getParent()->getParent();
   if (Subtarget.isTargetWin64() && MF->hasWinCFI()) {
     // Conditional tail calls confuse the Win64 unwinder.
     return false;


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