[llvm] Spill/restore FP/BP around instructions in which they are clobbered (PR #81048)

[via llvm-commits]

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@@ -0,0 +1,52 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc -mtriple=x86_64-pc-linux -stackrealign -spill-clobbered-fp=true -verify-machineinstrs < %s | FileCheck %s
+
+; Calling convention ghccc uses ebp to pass parameter, so calling a function
+; using ghccc clobbers ebp. We should save and restore ebp around such a call
+; if ebp is used as frame pointer.
+
+declare ghccc i32 @external(i32)
+
+define i32 @foo(i32 %0, i32 %1) {
+; CHECK-LABEL: foo:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    pushq %rbp
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    .cfi_offset %rbp, -16
+; CHECK-NEXT:    movq %rsp, %rbp
+; CHECK-NEXT:    .cfi_def_cfa_register %rbp
+; CHECK-NEXT:    pushq %r15
+; CHECK-NEXT:    pushq %r14
+; CHECK-NEXT:    pushq %r13
+; CHECK-NEXT:    pushq %r12
+; CHECK-NEXT:    pushq %rbx
+; CHECK-NEXT:    andq $-16, %rsp
+; CHECK-NEXT:    subq $16, %rsp
+; CHECK-NEXT:    .cfi_offset %rbx, -56
+; CHECK-NEXT:    .cfi_offset %r12, -48
+; CHECK-NEXT:    .cfi_offset %r13, -40
+; CHECK-NEXT:    .cfi_offset %r14, -32
+; CHECK-NEXT:    .cfi_offset %r15, -24
+; CHECK-NEXT:    # kill: def $edi killed $edi def $rdi
+; CHECK-NEXT:    pushq %rbp
+; CHECK-NEXT:    pushq %rax
+; CHECK-NEXT:    .cfi_remember_state
+; CHECK-NEXT:    .cfi_escape 0x0f, 0x06, 0x77, 0x08, 0x06, 0x11, 0x10, 0x22 #
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zmodem wrote:

If there's any stack manipulation after this (e.g. to pass more arguments to the call), I think the CFI would be incorrect? I'm not sure how we'd handle that though?

https://github.com/llvm/llvm-project/pull/81048