[ARM] Fix an off-by-one error when restoring LR for 16-bit Thumb

The commit https://reviews.llvm.org/rL318143 computes incorrectly to offset to
restore LR from.

The number of tPOP operands is 2 (condition) + 2 (implicit def and use of SP) +
count of the popped registers. We need to load LR from just past the last
register, hence the correct offset should be either getNumOperands() - 4 and
getNumExplicitOperands() - 2 (multiplied by 4).

Differential revision: https://reviews.llvm.org/D40305

llvm-svn: 319014

llvm/lib/Target/ARM/Thumb1FrameLowering.cpp

@@ -647,7 +647,7 @@ bool Thumb1FrameLowering::emitPopSpecialFixUp(MachineBasicBlock &MBB,
     BuildMI(MBB, MBBI, dl, TII.get(ARM::tLDRspi))
       .addReg(PopReg, RegState::Define)
       .addReg(ARM::SP)
-      .addImm(MBBI->getNumOperands() - 3)
+      .addImm(MBBI->getNumExplicitOperands() - 2)
       .add(predOps(ARMCC::AL));
     // Move from the temporary register to the LR.
     BuildMI(MBB, MBBI, dl, TII.get(ARM::tMOVr))

llvm/test/CodeGen/ARM/thumb1_return_sequence.ll

@@ -25,7 +25,7 @@ entry:
 ; --------
 ; Stack realignment means sp is restored from frame pointer
 ; CHECK-V4T:         mov sp
-; CHECK-V4T-NEXT:    ldr [[POP:r[4567]]], [sp, #{{.*}}]
+; CHECK-V4T-NEXT:    ldr [[POP:r[4567]]], [sp, #16]
 ; CHECK-V4T-NEXT:    mov lr, [[POP]]
 ; CHECK-V4T-NEXT:    pop {[[SAVED]]}
 ; CHECK-V4T-NEXT     add sp, sp, #4
@@ -57,14 +57,14 @@ entry:
 
 ; Epilogue
 ; --------
-; CHECK-V4T:         ldr [[POP:r[4567]]], [sp, #{{.*}}]
+; CHECK-V4T:         ldr [[POP:r[4567]]], [sp, #12]
 ; CHECK-V4T-NEXT:    mov lr, [[POP]]
 ; CHECK-V4T-NEXT:    pop {[[SAVED]]}
 ; CHECK-V4T-NEXT:    add sp, #16
 ; CHECK-V4T-NEXT:    bx  lr
 ; CHECK-V5T:         lsls r4
 ; CHECK-V5T-NEXT:    mov sp, r4
-; CHECK-V5T:         ldr [[POP:r[4567]]], [sp, #{{.*}}]
+; CHECK-V5T:         ldr [[POP:r[4567]]], [sp, #12]
 ; CHECK-V5T-NEXT:    mov lr, [[POP]]
 ; CHECK-V5T-NEXT:    pop {[[SAVED]]}
 ; CHECK-V5T-NEXT:    add sp, #16

llvm/test/CodeGen/ARM/v8m-tail-call.ll

@@ -8,7 +8,7 @@ define hidden i32 @f0() {
   %2 = tail call i32 @h0(i32 %1, i32 1, i32 2, i32 3)
   ret i32 %2
 ; CHECK-LABEL: f0
-; CHECK:      ldr     [[POP:r[4567]]], [sp
+; CHECK:      ldr     [[POP:r[4567]]], [sp, #4]
 ; CHECK-NEXT: mov     lr, [[POP]]
 ; CHECK-NEXT: pop     {{.*}}[[POP]]
 ; CHECK-NEXT: add     sp, #4
@@ -39,7 +39,7 @@ define hidden i32 @f2(i32, i32, i32, i32, i32) {
   %11 = phi i32 [ %9, %8 ], [ -1, %5 ]
   ret i32 %11
 ; CHECK-LABEL: f2
-; CHECK:      ldr     [[POP:r[4567]]], [sp
+; CHECK:      ldr     [[POP:r[4567]]], [sp, #12]
 ; CHECK-NEXT: mov     lr, [[POP]]
 ; CHECK-NEXT: pop     {{.*}}[[POP]]
 ; CHECK-NEXT: add     sp, #4

llvm/test/CodeGen/Thumb/thumb-shrink-wrapping.ll

@@ -647,7 +647,7 @@ define i1 @beq_to_bx(i32* %y, i32 %head) {
 ; ENABLE: push {r4, lr}
 
 ; CHECK: tst r3, r4
-; ENABLE-NEXT: ldr [[POP:r[4567]]], [sp, #8]
+; ENABLE-NEXT: ldr [[POP:r[4567]]], [sp, #4]
 ; ENABLE-NEXT: mov lr, [[POP]]
 ; ENABLE-NEXT: pop {[[POP]]}
 ; ENABLE-NEXT: add sp, #4