[llvm] [CFIFixup] Allow function prologues to span more than one basic block (PR #68984)

[Momchil Velikov via llvm-commits]

================
@@ -0,0 +1,308 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 3
+# RUN: llc -run-pass=cfi-fixup %s -o - | FileCheck %s
+--- |
+  source_filename = "cfi-fixup.ll"
+  target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+  target triple = "aarch64-linux"
+
+  define i32 @f(i32 %x) #0 {
+  entry:
+    %p = alloca i8, i32 30000, align 1
+    switch i32 %x, label %if.end7 [
+      i32 0, label %return
+      i32 1, label %if.then2
+      i32 2, label %if.then5
+    ]
+
+  if.then2:                                         ; preds = %entry
+    %call = tail call i32 @g1(i32 1)
+    %add = add nsw i32 %call, 1
+    br label %return
+
+  if.then5:                                         ; preds = %entry
+    %call6 = tail call i32 @g0(i32 2)
+    %sub = sub nsw i32 1, %call6
+    br label %return
+
+  if.end7:                                          ; preds = %entry
+    br label %return
+
+  return:                                           ; preds = %if.end7, %if.then5, %if.then2, %entry
+    %retval.0 = phi i32 [ %add, %if.then2 ], [ %sub, %if.then5 ], [ 0, %if.end7 ], [ 1, %entry ]
+    ret i32 %retval.0
+  }
+
+  declare i32 @g1(i32)
+
+  declare i32 @g0(i32)
+
+  attributes #0 = { uwtable "probe-stack"="inline-asm" }
+
+...
+---
+name:            f
+alignment:       4
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: true
+hasWinCFI:       false
+callsEHReturn:   false
+callsUnwindInit: false
+hasEHCatchret:   false
+hasEHScopes:     false
+hasEHFunclets:   false
+isOutlined:      false
+debugInstrRef:   false
+failsVerification: false
+tracksDebugUserValues: true
+registers:       []
+liveins:
+  - { reg: '$w0', virtual-reg: '' }
+frameInfo:
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       30016
+  offsetAdjustment: 0
+  maxAlignment:    8
+  adjustsStack:    true
+  hasCalls:        true
+  stackProtector:  ''
+  functionContext: ''
+  maxCallFrameSize: 0
+  cvBytesOfCalleeSavedRegisters: 0
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+  hasTailCall:     false
+  localFrameSize:  30000
+  savePoint:       ''
+  restorePoint:    ''
+fixedStack:      []
+stack:
+  - { id: 0, name: p, type: default, offset: -30016, size: 30000, alignment: 1,
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+      local-offset: -30000, debug-info-variable: '', debug-info-expression: '',
+      debug-info-location: '' }
+  - { id: 1, name: '', type: spill-slot, offset: -8, size: 8, alignment: 8,
+      stack-id: default, callee-saved-register: '$lr', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+  - { id: 2, name: '', type: spill-slot, offset: -16, size: 8, alignment: 8,
+      stack-id: default, callee-saved-register: '$fp', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+entry_values:    []
+callSites:       []
+debugValueSubstitutions: []
+constants:       []
+machineFunctionInfo:
+  hasRedZone:      false
+body:             |
+  ; CHECK-LABEL: name: f
+  ; CHECK: bb.0.entry:
+  ; CHECK-NEXT:   successors: %bb.1(0x80000000)
+  ; CHECK-NEXT:   liveins: $w0, $lr, $fp
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   early-clobber $sp = frame-setup STPXpre killed $fp, killed $lr, $sp, -2 :: (store (s64) into %stack.2), (store (s64) into %stack.1)
+  ; CHECK-NEXT:   frame-setup CFI_INSTRUCTION def_cfa_offset 16
+  ; CHECK-NEXT:   frame-setup CFI_INSTRUCTION offset $w30, -8
+  ; CHECK-NEXT:   frame-setup CFI_INSTRUCTION offset $w29, -16
+  ; CHECK-NEXT:   $x9 = frame-setup SUBXri $sp, 7, 12
+  ; CHECK-NEXT:   frame-setup CFI_INSTRUCTION def_cfa $w9, 28688
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.1.entry:
+  ; CHECK-NEXT:   successors: %bb.2(0x40000000), %bb.1(0x40000000)
+  ; CHECK-NEXT:   liveins: $x9
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   $sp = frame-setup SUBXri $sp, 1, 12
+  ; CHECK-NEXT:   $xzr = frame-setup SUBSXrx64 $sp, $x9, 24, implicit-def $nzcv
+  ; CHECK-NEXT:   frame-setup STRXui $xzr, $sp, 0
+  ; CHECK-NEXT:   frame-setup Bcc 1, %bb.1, implicit killed $nzcv
----------------
momchil-velikov wrote:

I don't think it would be useful.  Open coding stack probes is just the same old single-block prologue function, which has been working for quite a while and such a test would pass even without this patch.
The SCP patch series (many commits starting here https://github.com/llvm/llvm-project/pull/67123 , spread over several PRs themselves contain such tests, but for the purpose of testing SCP, it should affect CFIFixup.

https://github.com/llvm/llvm-project/pull/68984