[llvm] r251123 - [ARM CodeGen] @llvm.debugtrap call may be removed when restoring callee saved registers

[Oleg Ranevskyy via llvm-commits]

Author: oleg
Date: Fri Oct 23 12:17:59 2015
New Revision: 251123

URL: http://llvm.org/viewvc/llvm-project?rev=251123&view=rev
Log:
[ARM CodeGen] @llvm.debugtrap call may be removed when restoring callee saved registers

Summary:
When ARMFrameLowering::emitPopInst generates a "pop" instruction to restore the callee saved registers, it checks if the LR register is among them. If so, the function may decide to remove the basic block's terminator and replace it with a "pop" to the PC register instead of LR.

This leads to a problem when the block's terminator is preceded by a "llvm.debugtrap" call. The MI iterator points to the trap in such a case, which is also a terminator. If the function decides to restore LR to PC, it erroneously removes the trap.

Reviewers: asl, rengolin

Subscribers: aemerson, jfb, rengolin, dschuff, llvm-commits

Differential Revision: http://reviews.llvm.org/D13672

Added:
    llvm/trunk/test/CodeGen/ARM/debugtrap.ll
Modified:
    llvm/trunk/lib/Target/ARM/ARMFrameLowering.cpp

Modified: llvm/trunk/lib/Target/ARM/ARMFrameLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMFrameLowering.cpp?rev=251123&r1=251122&r2=251123&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMFrameLowering.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMFrameLowering.cpp Fri Oct 23 12:17:59 2015
@@ -968,12 +968,16 @@ void ARMFrameLowering::emitPopInst(Machi
   DebugLoc DL;
   bool isTailCall = false;
   bool isInterrupt = false;
+  bool isTrap = false;
   if (MBB.end() != MI) {
     DL = MI->getDebugLoc();
     unsigned RetOpcode = MI->getOpcode();
     isTailCall = (RetOpcode == ARM::TCRETURNdi || RetOpcode == ARM::TCRETURNri);
     isInterrupt =
         RetOpcode == ARM::SUBS_PC_LR || RetOpcode == ARM::t2SUBS_PC_LR;
+    isTrap =
+        RetOpcode == ARM::TRAP || RetOpcode == ARM::TRAPNaCl ||
+        RetOpcode == ARM::tTRAP;
   }
 
   SmallVector<unsigned, 4> Regs;
@@ -990,7 +994,7 @@ void ARMFrameLowering::emitPopInst(Machi
         continue;
 
       if (Reg == ARM::LR && !isTailCall && !isVarArg && !isInterrupt &&
-          STI.hasV5TOps()) {
+          !isTrap && STI.hasV5TOps()) {
         if (MBB.succ_empty()) {
           Reg = ARM::PC;
           DeleteRet = true;

Added: llvm/trunk/test/CodeGen/ARM/debugtrap.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/debugtrap.ll?rev=251123&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/debugtrap.ll (added)
+++ llvm/trunk/test/CodeGen/ARM/debugtrap.ll Fri Oct 23 12:17:59 2015
@@ -0,0 +1,17 @@
+; This test ensures the @llvm.debugtrap() call is not removed when generating
+; the 'pop' instruction to restore the callee saved registers on ARM.
+
+; RUN: llc < %s -mtriple=armv7 -O0 -filetype=asm | FileCheck %s 
+
+declare void @llvm.debugtrap() nounwind
+declare void @foo() nounwind
+
+define void @test() nounwind {
+entry:
+  ; CHECK: bl foo
+  ; CHECK-NEXT: pop
+  ; CHECK-NEXT: trap
+  call void @foo()
+  call void @llvm.debugtrap()
+  ret void
+}