[llvm] r199266 - ARM: correctly determine final tBX_LR in Thumb1 functions

[Tim Northover]

Author: tnorthover
Date: Tue Jan 14 16:53:28 2014
New Revision: 199266

URL: http://llvm.org/viewvc/llvm-project?rev=199266&view=rev
Log:
ARM: correctly determine final tBX_LR in Thumb1 functions

The changes caused by folding an sp-adjustment into a "pop" previously
disrupted the forward search for the final real instruction in a
terminating block. This switches to a backward search (skipping debug
instrs).

This fixes PR18399.

Patch by Zhaoshi.

Modified:
    llvm/trunk/lib/Target/ARM/Thumb1FrameLowering.cpp
    llvm/trunk/test/CodeGen/ARM/fold-stack-adjust.ll

Modified: llvm/trunk/lib/Target/ARM/Thumb1FrameLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/Thumb1FrameLowering.cpp?rev=199266&r1=199265&r2=199266&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/Thumb1FrameLowering.cpp (original)
+++ llvm/trunk/lib/Target/ARM/Thumb1FrameLowering.cpp Tue Jan 14 16:53:28 2014
@@ -304,9 +304,9 @@ void Thumb1FrameLowering::emitEpilogue(M
     // we need to update the SP after popping the value. Therefore, we
     // pop the old LR into R3 as a temporary.
 
-    // Move back past the callee-saved register restoration
-    while (MBBI != MBB.end() && isCSRestore(MBBI, CSRegs))
-      ++MBBI;
+    // Get the last instruction, tBX_RET
+    MBBI = MBB.getLastNonDebugInstr();
+    assert (MBBI->getOpcode() == ARM::tBX_RET);
     // Epilogue for vararg functions: pop LR to R3 and branch off it.
     AddDefaultPred(BuildMI(MBB, MBBI, dl, TII.get(ARM::tPOP)))
       .addReg(ARM::R3, RegState::Define);

Modified: llvm/trunk/test/CodeGen/ARM/fold-stack-adjust.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/fold-stack-adjust.ll?rev=199266&r1=199265&r2=199266&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/fold-stack-adjust.ll (original)
+++ llvm/trunk/test/CodeGen/ARM/fold-stack-adjust.ll Tue Jan 14 16:53:28 2014
@@ -162,3 +162,26 @@ end:
   ; the correct edge-case (first inst in block is correct one to adjust).
   ret void
 }
+
+define void @test_varsize(...) minsize {
+; CHECK-T1-LABEL: test_varsize:
+; CHECK-T1: sub	sp, #16
+; CHECK-T1: push	{r2, r3, r4, r5, r7, lr}
+; ...
+; CHECK-T1: pop	{r2, r3, r4, r5, r7}
+; CHECK-T1: pop	{r3}
+; CHECK-T1: add	sp, #16
+; CHECK-T1: bx	r3
+
+; CHECK-LABEL: test_varsize:
+; CHECK: sub	sp, #16
+; CHECK: push	{r5, r6, r7, lr}
+; ...
+; CHECK: pop.w	{r2, r3, r7, lr}
+; CHECK: add	sp, #16
+; CHECK: bx	lr
+
+  %var = alloca i8, i32 8
+  call void @bar(i8* %var)
+  ret void
+}