[llvm] r290091 - [XRay] Fix assertion failure on empty machine basic blocks (PR 31424)

[Dean Michael Berris via llvm-commits]

Author: dberris
Date: Mon Dec 19 03:20:38 2016
New Revision: 290091

URL: http://llvm.org/viewvc/llvm-project?rev=290091&view=rev
Log:
[XRay] Fix assertion failure on empty machine basic blocks (PR 31424)

The original version of the code in XRayInstrumentation.cpp assumed that
functions may not have empty machine basic blocks (or that the first one
couldn't be). This change addresses that by special-casing that specific
situation.

We provide two .mir test-cases to make sure we're handling this
appropriately.

Fixes llvm.org/PR31424.

Reviewers: chandlerc

Subscribers: varno, llvm-commits

Differential Revision: https://reviews.llvm.org/D27913

Added:
    llvm/trunk/test/CodeGen/X86/xray-empty-firstmbb.mir
    llvm/trunk/test/CodeGen/X86/xray-empty-function.mir
Modified:
    llvm/trunk/lib/CodeGen/XRayInstrumentation.cpp

Modified: llvm/trunk/lib/CodeGen/XRayInstrumentation.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/XRayInstrumentation.cpp?rev=290091&r1=290090&r2=290091&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/XRayInstrumentation.cpp (original)
+++ llvm/trunk/lib/CodeGen/XRayInstrumentation.cpp Mon Dec 19 03:20:38 2016
@@ -129,7 +129,15 @@ bool XRayInstrumentation::runOnMachineFu
       return false; // Function is too small.
   }
 
-  auto &FirstMBB = *MF.begin();
+  // We look for the first non-empty MachineBasicBlock, so that we can insert
+  // the function instrumentation in the appropriate place.
+  auto MBI =
+      find_if(MF, [&](const MachineBasicBlock &MBB) { return !MBB.empty(); });
+  if (MBI == MF.end())
+    return false; // The function is empty.
+
+  auto *TII = MF.getSubtarget().getInstrInfo();
+  auto &FirstMBB = *MBI;
   auto &FirstMI = *FirstMBB.begin();
 
   if (!MF.getSubtarget().isXRaySupported()) {
@@ -142,7 +150,6 @@ bool XRayInstrumentation::runOnMachineFu
 
   // First, insert an PATCHABLE_FUNCTION_ENTER as the first instruction of the
   // MachineFunction.
-  auto *TII = MF.getSubtarget().getInstrInfo();
   BuildMI(FirstMBB, FirstMI, FirstMI.getDebugLoc(),
           TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER));
 

Added: llvm/trunk/test/CodeGen/X86/xray-empty-firstmbb.mir
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/xray-empty-firstmbb.mir?rev=290091&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/xray-empty-firstmbb.mir (added)
+++ llvm/trunk/test/CodeGen/X86/xray-empty-firstmbb.mir Mon Dec 19 03:20:38 2016
@@ -0,0 +1,23 @@
+# RUN: llc -run-pass xray-instrumentation -mtriple=x86_64-unknown-linux-gnu -o - %s | FileCheck %s
+#
+# Make sure we can handle empty first basic blocks.
+
+--- |
+
+  define i32 @foo() noinline uwtable "xray-instruction-threshold"="1" {
+  entry:
+    unreachable
+  }
+
+...
+
+---
+name: foo
+tracksRegLiveness: true
+liveins:
+  - { reg: '%edi'}
+body:            |
+  bb.0.entry:
+    liveins: %edi
+    ; CHECK-NOT: PATCHABLE_FUNCTION_ENTER
+...

Added: llvm/trunk/test/CodeGen/X86/xray-empty-function.mir
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/xray-empty-function.mir?rev=290091&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/xray-empty-function.mir (added)
+++ llvm/trunk/test/CodeGen/X86/xray-empty-function.mir Mon Dec 19 03:20:38 2016
@@ -0,0 +1,13 @@
+# RUN: llc -run-pass xray-instrumentation -mtriple=x86_64-unknown-linux-gnu -o - %s | FileCheck %s
+#
+# Make sure we can handle empty functions.
+---
+name: empty
+tracksRegLiveness: true
+liveins:
+  - { reg: '%edi'}
+body:            |
+  bb.0:
+    ; CHECK-NOT: PATCHABLE_FUNCTION_ENTER
+...
+