[llvm] [X86] nocf_check: disable tail call (PR #131487)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay updated https://github.com/llvm/llvm-project/pull/131487

>From 5d110b34bcefc4b0016c0bb75011db0a15ea729a Mon Sep 17 00:00:00 2001
From: Fangrui Song <i at maskray.me>
Date: Sat, 15 Mar 2025 20:32:13 -0700
Subject: [PATCH 1/2] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20in?=
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Created using spr 1.3.5-bogner
---
 llvm/lib/Target/X86/X86ISelLoweringCall.cpp | 12 ++++++++---
 llvm/test/CodeGen/X86/nocf_check.ll         | 23 +++++++++++++++++++++
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ISelLoweringCall.cpp b/llvm/lib/Target/X86/X86ISelLoweringCall.cpp
index 80b4aeeda1e00..76451994bb73b 100644
--- a/llvm/lib/Target/X86/X86ISelLoweringCall.cpp
+++ b/llvm/lib/Target/X86/X86ISelLoweringCall.cpp
@@ -2034,11 +2034,17 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   X86MachineFunctionInfo *X86Info = MF.getInfo<X86MachineFunctionInfo>();
   bool HasNCSR = (CB && isa<CallInst>(CB) &&
                   CB->hasFnAttr("no_caller_saved_registers"));
-  bool HasNoCfCheck = (CB && CB->doesNoCfCheck());
   bool IsIndirectCall = (CB && isa<CallInst>(CB) && CB->isIndirectCall());
   bool IsCFICall = IsIndirectCall && CLI.CFIType;
   const Module *M = MF.getFunction().getParent();
-  Metadata *IsCFProtectionSupported = M->getModuleFlag("cf-protection-branch");
+
+  // If the indirect call target has the nocf_check attribute, the call needs
+  // the NOTRACK prefix. For simplicity just disable tail calls as there there
+  // are too many variants
+  bool IsNoTrackIndirectCall = IsIndirectCall && CB->doesNoCfCheck() &&
+                               M->getModuleFlag("cf-protection-branch");
+  if (IsNoTrackIndirectCall)
+    isTailCall = false;
 
   MachineFunction::CallSiteInfo CSInfo;
   if (CallConv == CallingConv::X86_INTR)
@@ -2549,7 +2555,7 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
 
   // Returns a chain & a glue for retval copy to use.
   SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
-  if (HasNoCfCheck && IsCFProtectionSupported && IsIndirectCall) {
+  if (IsNoTrackIndirectCall) {
     Chain = DAG.getNode(X86ISD::NT_CALL, dl, NodeTys, Ops);
   } else if (CLI.CB && objcarc::hasAttachedCallOpBundle(CLI.CB)) {
     // Calls with a "clang.arc.attachedcall" bundle are special. They should be
diff --git a/llvm/test/CodeGen/X86/nocf_check.ll b/llvm/test/CodeGen/X86/nocf_check.ll
index d6c6edea55e14..7b184edf8c0b0 100644
--- a/llvm/test/CodeGen/X86/nocf_check.ll
+++ b/llvm/test/CodeGen/X86/nocf_check.ll
@@ -43,6 +43,29 @@ entry:
   ret void
 }
 
+;; NOTRACK tail call is not implemented, so nocf_check just disables tail call.
+define void @NoCfCheckTail(ptr %p) #1 {
+; CHECK-LABEL: NoCfCheckTail:
+; CHECK:       notrack callq *%rax
+  %f = load ptr, ptr %p, align 4
+  tail call void %f() #2
+  ret void
+}
+
+define void @NoCfCheckTailCond(ptr %f, i1 %x) #1 {
+; CHECK-LABEL: NoCfCheckTailCond:
+; CHECK:       notrack callq *%rdi
+; CHECK:       notrack callq *%rdi
+entry:
+  br i1 %x, label %bb1, label %bb2
+bb1:
+  tail call void %f() #2
+  ret void
+bb2:
+  tail call void %f() #2
+  ret void
+}
+
 attributes #0 = { nocf_check noinline nounwind optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" "unsafe-fp-math"="false" "use-soft-float"="false" }
 attributes #1 = { noinline nounwind optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" "unsafe-fp-math"="false" "use-soft-float"="false" }
 attributes #2 = { nocf_check }

>From 27631f17399363ec1c50a01a64991bc443262d58 Mon Sep 17 00:00:00 2001
From: Fangrui Song <i at maskray.me>
Date: Sat, 15 Mar 2025 20:35:22 -0700
Subject: [PATCH 2/2] .

Created using spr 1.3.5-bogner
---
 llvm/lib/Target/X86/X86ISelLoweringCall.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ISelLoweringCall.cpp b/llvm/lib/Target/X86/X86ISelLoweringCall.cpp
index 76451994bb73b..739a29283b41c 100644
--- a/llvm/lib/Target/X86/X86ISelLoweringCall.cpp
+++ b/llvm/lib/Target/X86/X86ISelLoweringCall.cpp
@@ -2039,8 +2039,8 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   const Module *M = MF.getFunction().getParent();
 
   // If the indirect call target has the nocf_check attribute, the call needs
-  // the NOTRACK prefix. For simplicity just disable tail calls as there there
-  // are too many variants
+  // the NOTRACK prefix. For simplicity just disable tail calls as there are
+  // so many variants.
   bool IsNoTrackIndirectCall = IsIndirectCall && CB->doesNoCfCheck() &&
                                M->getModuleFlag("cf-protection-branch");
   if (IsNoTrackIndirectCall)