[llvm] [ShrinkWrap] Modify shrink wrapping to accommodate functions terminated by no-return blocks (PR #167548)

[Alex Bradbury via llvm-commits]

asb wrote:

I'll get a proper .ll reproducer tomorrow, but here's the .s diff for llvm-ar that is causing the issue:

```asm
--- ./tools/llvm-ar/CMakeFiles/llvm-ar.dir/llvm-ar.s    2025-11-27 19:02:12.188502784 +0000
+++ ../stage2.bad/./tools/llvm-ar/CMakeFiles/llvm-ar.dir/llvm-ar.s      2025-11-27 19:36:01.525297430 +00
00
@@ -6379,25 +6379,17 @@
 _ZL11failIfErrorSt10error_codeN4llvm5TwineE: # @_ZL11failIfErrorSt10error_codeN4llvm5TwineE
        .cfi_startproc
 # %bb.0:                                # %entry
+       sext.w  a0, a0
+       bnez    a0, .LBB24_2
+# %bb.1:                                # %if.then
+       ret
+.LBB24_2:                               # %if.end
        addi    sp, sp, -304
        .cfi_def_cfa_offset 304
        sd      ra, 296(sp)                     # 8-byte Folded Spill
        sd      s0, 288(sp)                     # 8-byte Folded Spill
        .cfi_offset ra, -8
        .cfi_offset s0, -16
-       .cfi_remember_state
-       sext.w  a0, a0
-       bnez    a0, .LBB24_2
-# %bb.1:                                # %if.then
-       ld      ra, 296(sp)                     # 8-byte Folded Reload
-       ld      s0, 288(sp)                     # 8-byte Folded Reload
-       .cfi_restore ra
-       .cfi_restore s0
-       addi    sp, sp, 304
-       .cfi_def_cfa_offset 0
-       ret
-.LBB24_2:                               # %if.end
-       .cfi_restore_state
        sd      a1, 8(sp)                       # 8-byte Folded Spill
        sd      a0, 16(sp)                      # 8-byte Folded Spill
        addi    a0, sp, 256
@@ -6405,6 +6397,12 @@
        mv      a1, a2
        call    _ZNK4llvm5Twine3strB5cxx11Ev
        ld      a0, 264(sp)
+       ld      ra, 296(sp)                     # 8-byte Folded Reload
+       ld      s0, 288(sp)                     # 8-byte Folded Reload
+       .cfi_restore ra
+       .cfi_restore s0
+       addi    sp, sp, 304
+       .cfi_def_cfa_offset 0
        bnez    a0, .LBB24_4
 # %bb.3:                                # %if.then2
        ld      a1, 8(sp)                       # 8-byte Folded Reload

```
At the end of `LBB24_2` in the 'bad' version, the stack is deallocated but then it's accessed in the fallthrough to ` # %bb.3:`                       

https://github.com/llvm/llvm-project/pull/167548