[xray] Honor xray-never function-instrument attribute

[ianlevesque]

Summary

function-instrument=xray-never wasn't actually honored before. We were getting lucky that it worked because CodeGenFunction would omit the other xray attributes when a function as annotated with xray_never_instrument. This patch adds proper support.

[dberris]

Do you think we should fix this by handling the xray-never attribute in XRayInstrumentation, or having CodeGenFunction remove the threshold if xray-never is set?

Good catch, thanks!

I think we should go with the former (handling the case in XRayInstrumentation) -- the rationale here is that when we apply the file-based always-instrument case, we ignore the "never" attribute (i.e. the "always" case overrides the "never" case). We should make sure that this case still works (if we don't have cases for that, then we should add those too).

[ianlevesque]

Apply the fix in XRayInstrumentation, add test cases.

[dberris]

LGTM -- thanks!

llvm/lib/CodeGen/XRayInstrumentation.cpp

for (auto &MBB : MF)
     }
 }
 
 bool XRayInstrumentation::runOnMachineFunction(MachineFunction &MF) {
   auto &F = MF.getFunction();
   auto InstrAttr = F.getFnAttribute("function-instrument");
   bool AlwaysInstrument = InstrAttr.isStringAttribute() &&
                           InstrAttr.getValueAsString() == "xray-always";
+  bool NeverInstrument = InstrAttr.isStringAttribute() &&
+                         InstrAttr.getValueAsString() == "xray-never";
+  if (NeverInstrument && !AlwaysInstrument)
+    return false;
   auto ThresholdAttr = F.getFnAttribute("xray-instruction-threshold");
   auto IgnoreLoopsAttr = F.getFnAttribute("xray-ignore-loops");
   unsigned int XRayThreshold = 0;
   if (!AlwaysInstrument) {
     if (!ThresholdAttr.isStringAttribute())
       return false; // XRay threshold attribute not found.
     if (ThresholdAttr.getValueAsString().getAsInteger(10, XRayThreshold))
       return false; // Invalid value for threshold.

llvm/test/CodeGen/AArch64/xray-attribute-instrumentation.ll

 ; RUN: llc -filetype=asm -o - -mtriple=aarch64-unknown-linux-gnu < %s | FileCheck %s
 
 define i32 @foo() nounwind noinline uwtable "function-instrument"="xray-always" {
+; CHECK-LABEL: foo:
 ; CHECK-LABEL: Lxray_sled_0:
 ; CHECK-NEXT:  b  #32
 ; CHECK-NEXT:  nop
 ; CHECK-NEXT:  nop
 ; CHECK-NEXT:  nop
 ; CHECK-NEXT:  nop
 ; CHECK-NEXT:  nop
 ; CHECK-NEXT:  nop
 ; CHECK-NEXT:  nop
 ; CHECK-LABEL: Ltmp0:
   ret i32 0
 ; CHECK-LABEL: Lxray_sled_1:
 ; CHECK-NEXT:  b  #32
 ; CHECK-NEXT:  nop
 ; CHECK-NEXT:  nop
 ; CHECK-NEXT:  nop
 ; CHECK-NEXT:  nop
 ; CHECK-NEXT:  nop
 ; CHECK-NEXT:  nop
 ; CHECK-NEXT:  nop
 ; CHECK-LABEL: Ltmp1:
 ; CHECK-NEXT:  ret
 }
+
 ; CHECK-LABEL: xray_instr_map
 ; CHECK-LABEL: Lxray_sleds_start0
 ; CHECK:       .xword .Lxray_sled_0
 ; CHECK:       .xword .Lxray_sled_1
 ; CHECK-LABEL: Lxray_sleds_end0
+
+define i32 @bar() nounwind noinline uwtable "function-instrument"="xray-never" "function-instrument"="xray-always" {
+; CHECK-LABEL: bar:
+; CHECK-LABEL: Lxray_sled_2:
+; CHECK-NEXT:  b  #32
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-LABEL: Ltmp4:
+  ret i32 0
+; CHECK-LABEL: Lxray_sled_3:
+; CHECK-NEXT:  b  #32
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-LABEL: Ltmp5:
+; CHECK-NEXT:  ret
+}
+
+; CHECK-LABEL: xray_instr_map
+; CHECK-LABEL: Lxray_sleds_start1
+; CHECK:       .xword .Lxray_sled_2
+; CHECK:       .xword .Lxray_sled_3
+; CHECK-LABEL: Lxray_sleds_end1
+
+define i32 @instrumented() nounwind noinline uwtable "xray-instruction-threshold"="1" {
+; CHECK-LABEL: instrumented:
+; CHECK-LABEL: Lxray_sled_4:
+; CHECK-NEXT:  b  #32
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-LABEL: Ltmp8:
+  ret i32 0
+; CHECK-LABEL: Lxray_sled_5:
+; CHECK-NEXT:  b  #32
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-NEXT:  nop
+; CHECK-LABEL: Ltmp9:
+; CHECK-NEXT:  ret
+}
+
+; CHECK-LABEL: xray_instr_map
+; CHECK-LABEL: Lxray_sleds_start2
+; CHECK:       .xword .Lxray_sled_4
+; CHECK:       .xword .Lxray_sled_5
+; CHECK-LABEL: Lxray_sleds_end2
+
+define i32 @not_instrumented() nounwind noinline uwtable "xray-instruction-threshold"="1" "function-instrument"="xray-never" {
+; CHECK-LABEL: not_instrumented
+; CHECK-NOT: .Lxray_sled_6
+  ret i32 0
+; CHECK:  ret
+}