[llvm] 7628e47 - [xray] Add xray-ignore-loops option

[Shoaib Meenai via llvm-commits]

Author: Ian Levesque
Date: 2020-01-17T13:32:17-08:00
New Revision: 7628e474a5916ed8a43c015248443f4c03077509

URL: https://github.com/llvm/llvm-project/commit/7628e474a5916ed8a43c015248443f4c03077509
DIFF: https://github.com/llvm/llvm-project/commit/7628e474a5916ed8a43c015248443f4c03077509.diff

LOG: [xray] Add xray-ignore-loops option

XRay allows tuning by minimum function size, but also always instruments
functions with loops in them.  If the minimum function size is set to a
large value the loop instrumention ends up causing most functions to be
instrumented anyway.  This adds a new flag, xray-ignore-loops, to disable
the loop detection logic.

Differential Revision: https://reviews.llvm.org/D72659

Added: 
    llvm/test/CodeGen/X86/xray-ignore-loop-detection.ll

Modified: 
    llvm/lib/CodeGen/XRayInstrumentation.cpp
    llvm/test/CodeGen/X86/xray-loop-detection.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/XRayInstrumentation.cpp b/llvm/lib/CodeGen/XRayInstrumentation.cpp
index 4847a0c3e842..a7ccfba1a2fc 100644
--- a/llvm/lib/CodeGen/XRayInstrumentation.cpp
+++ b/llvm/lib/CodeGen/XRayInstrumentation.cpp
@@ -148,40 +148,51 @@ bool XRayInstrumentation::runOnMachineFunction(MachineFunction &MF) {
   bool AlwaysInstrument = !InstrAttr.hasAttribute(Attribute::None) &&
                           InstrAttr.isStringAttribute() &&
                           InstrAttr.getValueAsString() == "xray-always";
-  Attribute Attr = F.getFnAttribute("xray-instruction-threshold");
-  unsigned XRayThreshold = 0;
+  auto ThresholdAttr = F.getFnAttribute("xray-instruction-threshold");
+  auto IgnoreLoopsAttr = F.getFnAttribute("xray-ignore-loops");
+  unsigned int XRayThreshold = 0;
   if (!AlwaysInstrument) {
-    if (Attr.hasAttribute(Attribute::None) || !Attr.isStringAttribute())
+    if (ThresholdAttr.hasAttribute(Attribute::None) ||
+        !ThresholdAttr.isStringAttribute())
       return false; // XRay threshold attribute not found.
-    if (Attr.getValueAsString().getAsInteger(10, XRayThreshold))
+    if (ThresholdAttr.getValueAsString().getAsInteger(10, XRayThreshold))
       return false; // Invalid value for threshold.
 
+    bool IgnoreLoops = !IgnoreLoopsAttr.hasAttribute(Attribute::None);
+
     // Count the number of MachineInstr`s in MachineFunction
     int64_t MICount = 0;
     for (const auto &MBB : MF)
       MICount += MBB.size();
 
-    // Get MachineDominatorTree or compute it on the fly if it's unavailable
-    auto *MDT = getAnalysisIfAvailable<MachineDominatorTree>();
-    MachineDominatorTree ComputedMDT;
-    if (!MDT) {
-      ComputedMDT.getBase().recalculate(MF);
-      MDT = &ComputedMDT;
-    }
+    bool TooFewInstrs = MICount < XRayThreshold;
 
-    // Get MachineLoopInfo or compute it on the fly if it's unavailable
-    auto *MLI = getAnalysisIfAvailable<MachineLoopInfo>();
-    MachineLoopInfo ComputedMLI;
-    if (!MLI) {
-      ComputedMLI.getBase().analyze(MDT->getBase());
-      MLI = &ComputedMLI;
-    }
+    if (!IgnoreLoops) {
+      // Get MachineDominatorTree or compute it on the fly if it's unavailable
+      auto *MDT = getAnalysisIfAvailable<MachineDominatorTree>();
+      MachineDominatorTree ComputedMDT;
+      if (!MDT) {
+        ComputedMDT.getBase().recalculate(MF);
+        MDT = &ComputedMDT;
+      }
 
-    // Check if we have a loop.
-    // FIXME: Maybe make this smarter, and see whether the loops are dependent
-    // on inputs or side-effects?
-    if (MLI->empty() && MICount < XRayThreshold)
-      return false; // Function is too small and has no loops.
+      // Get MachineLoopInfo or compute it on the fly if it's unavailable
+      auto *MLI = getAnalysisIfAvailable<MachineLoopInfo>();
+      MachineLoopInfo ComputedMLI;
+      if (!MLI) {
+        ComputedMLI.getBase().analyze(MDT->getBase());
+        MLI = &ComputedMLI;
+      }
+
+      // Check if we have a loop.
+      // FIXME: Maybe make this smarter, and see whether the loops are dependent
+      // on inputs or side-effects?
+      if (MLI->empty() && TooFewInstrs)
+        return false; // Function is too small and has no loops.
+    } else if (TooFewInstrs) {
+      // Function is too small
+      return false;
+    }
   }
 
   // We look for the first non-empty MachineBasicBlock, so that we can insert

diff  --git a/llvm/test/CodeGen/X86/xray-ignore-loop-detection.ll b/llvm/test/CodeGen/X86/xray-ignore-loop-detection.ll
new file mode 100644
index 000000000000..2450d991e3aa
--- /dev/null
+++ b/llvm/test/CodeGen/X86/xray-ignore-loop-detection.ll
@@ -0,0 +1,19 @@
+; RUN: llc -verify-machineinstrs -filetype=asm -o - -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
+; RUN: llc -verify-machineinstrs -filetype=asm -o - -mtriple=x86_64-darwin-unknown    < %s | FileCheck %s
+
+define i32 @foo(i32 %i) nounwind noinline uwtable "xray-instruction-threshold"="10" "xray-ignore-loops" {
+entry:
+  br label %Test
+Test:
+  %indvar = phi i32 [0, %entry], [%nextindvar, %Inc]
+  %cond = icmp eq i32 %indvar, %i
+  br i1 %cond, label %Exit, label %Inc
+Inc:
+  %nextindvar = add i32 %indvar, 1
+  br label %Test
+Exit:
+  %retval = phi i32 [%indvar, %Test]
+  ret i32 %retval
+}
+
+; CHECK-NOT: xray_sled_0:

diff  --git a/llvm/test/CodeGen/X86/xray-loop-detection.ll b/llvm/test/CodeGen/X86/xray-loop-detection.ll
index c47592eef021..4acb22983be3 100644
--- a/llvm/test/CodeGen/X86/xray-loop-detection.ll
+++ b/llvm/test/CodeGen/X86/xray-loop-detection.ll
@@ -1,7 +1,7 @@
 ; RUN: llc -verify-machineinstrs -filetype=asm -o - -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
 ; RUN: llc -verify-machineinstrs -filetype=asm -o - -mtriple=x86_64-darwin-unknown    < %s | FileCheck %s
 
-define i32 @foo(i32 %i) nounwind noinline uwtable "xray-instruction-threshold"="1" {
+define i32 @foo(i32 %i) nounwind noinline uwtable "xray-instruction-threshold"="10" {
 entry:
   br label %Test
 Test: