[ARM] Handle t2ADDri in ARMAsmPrinter::EmitUnwindingInstruction

[ahatanak]

Summary

This fixes a bug in ARMAsmPrinter::EmitUnwindingInstruction where llvm_unreachable was reached because t2ADDri wasn't handled.

It looks like this crash could also have been avoided if the function checked MAI->getExceptionHandlingType() (and returned early), but it looks like the case clause for t2ADDri should be added regardless of that.

[t.p.northover]

Hi Akira,

The code change looks fine, but the test is quite a bit more complicated than it needs to be. The key points triggering this error are:

• A frame pointer is required and is r11 (so that t2ADD is used)
• sp != fp

I believe this is a reasonably minimal example (using the normal call to ensure the FP isn't eliminated and the asm to make sure at least one callee-saved register is used):

define void @foo1() {
  call void asm sideeffect "", "~{r4}"()
  call void @foo2()
  ret void
}
declare void @foo2()

[ahatanak]

Thanks Tim. Your minimal test case is indeed sufficient to trigger the crash. I'll update the test case and commit the patch shortly.

lib/Target/ARM/ARMAsmPrinter.cpp

if (SrcReg == ARM::SP) {
       default:
         MI->dump();
         llvm_unreachable("Unsupported opcode for unwinding information");
       case ARM::MOVr:
       case ARM::tMOVr:
         Offset = 0;
         break;
       case ARM::ADDri:
+      case ARM::t2ADDri:
         Offset = -MI->getOperand(2).getImm();
         break;
       case ARM::SUBri:
       case ARM::t2SUBri:
         Offset = MI->getOperand(2).getImm();
         break;
       case ARM::tSUBspi:
         Offset = MI->getOperand(2).getImm()*4;

test/CodeGen/Thumb2/emit-unwinding.ll

+; RUN: llc -mtriple thumbv7em-apple-unknown-eabi-macho %s -o - -O0 -disable-fp-elim | FileCheck %s
+
+; CHECK: add.w r11, sp, #{{[1-9]+}}
+
+define i32 @foo1(i32 %n) {
+entry:
+  %n.addr = alloca i32, align 4
+  %a1 = alloca [256 x i32], align 4
+  store i32 %n, i32* %n.addr, align 4
+  %arraydecay = getelementptr inbounds [256 x i32], [256 x i32]* %a1, i32 0, i32 0
+  call void @foo2(i32* %arraydecay)
+  call void asm sideeffect "", "~{r4}"() #2
+  %0 = load i32, i32* %n.addr, align 4
+  %arrayidx = getelementptr inbounds [256 x i32], [256 x i32]* %a1, i32 0, i32 %0
+  %1 = load i32, i32* %arrayidx, align 4
+  %arrayidx1 = getelementptr inbounds [256 x i32], [256 x i32]* %a1, i32 0, i32 1
+  %2 = load i32, i32* %arrayidx1, align 4
+  %add = add nsw i32 %1, %2
+  ret i32 %add
+}
+
+declare void @foo2(i32*)