Frame pointer clobbered when restoring callee-saved registers

[dylanmckay]

Discovered while working on #38.

I've found a problem which causes Y to be clobbered before function epilogue .

The function emission code looks something like this

• Emit function prologue
• Restore callee saved registers
• Emit function epilogue

It looks like Y is automatically restored before the epilogue is generated. The epilogue assumes that 'Y' still contains SP, but it in actual fact contains its original value at the time the function was called.

This should be an easy fix.

I've been using the same testcase as in #38, shown here

interrupt.ll

; ModuleID = 'interrupt.cgu-0.rs'
source_filename = "interrupt.cgu-0.rs"
target datalayout = "e-p:16:16:16-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-n8"
target triple = "avr-atmel-none"

@__rustc_debug_gdb_scripts_section__ = internal unnamed_addr constant [34 x i8] c"\01gdb_load_rust_pretty_printers.py\00", section ".debug_gdb_scripts", align 1

; Function Attrs: nounwind uwtable
define void @main() unnamed_addr #0 !dbg !5 {
start:
  %tmp_ret2 = alloca i8
  %tmp_ret1 = alloca i8
  %tmp_ret = alloca i8
  %0 = load volatile i8, i8* inttoptr (i16 36 to i8*), align 1, !dbg !10
  store i8 %0, i8* %tmp_ret, !dbg !10
  %1 = load i8, i8* %tmp_ret, !dbg !10
  br label %bb1, !dbg !10

bb1:                                              ; preds = %start
  %2 = or i8 %1, 32, !dbg !10
  store volatile i8 %2, i8* inttoptr (i16 36 to i8*), align 1, !dbg !10
  br label %bb2, !dbg !10

bb2:                                              ; preds = %bb1
  %3 = load volatile i8, i8* inttoptr (i16 129 to i8*), align 1, !dbg !11
  store i8 %3, i8* %tmp_ret1, !dbg !11
  %4 = load i8, i8* %tmp_ret1, !dbg !11
  br label %bb3, !dbg !11

bb3:                                              ; preds = %bb2
  %5 = or i8 %4, 13, !dbg !11
  store volatile i8 %5, i8* inttoptr (i16 129 to i8*), align 1, !dbg !11
  br label %bb4, !dbg !11

bb4:                                              ; preds = %bb3
  store volatile i16 -3036, i16* inttoptr (i16 136 to i16*), align 2, !dbg !12
  br label %bb5, !dbg !12

bb5:                                              ; preds = %bb4
  %6 = load volatile i8, i8* inttoptr (i16 111 to i8*), align 1, !dbg !13
  store i8 %6, i8* %tmp_ret2, !dbg !13
  %7 = load i8, i8* %tmp_ret2, !dbg !13
  br label %bb6, !dbg !13

bb6:                                              ; preds = %bb5
  %8 = or i8 %7, 2, !dbg !13
  store volatile i8 %8, i8* inttoptr (i16 111 to i8*), align 1, !dbg !13
  br label %bb7, !dbg !13

bb7:                                              ; preds = %bb6
  call void asm "SEI", ""(), !dbg !14, !srcloc !15
  br label %bb8, !dbg !16

bb8:                                              ; preds = %bb8, %bb7
  br label %bb8, !dbg !16
}

; Function Attrs: nounwind uwtable
define avr_signalcc  void @__vector_11() unnamed_addr #0 !dbg !17 {
start:
  %tmp_ret = alloca i8
  %0 = load volatile i8, i8* inttoptr (i16 37 to i8*), align 1, !dbg !18
  store i8 %0, i8* %tmp_ret, !dbg !18
  %1 = load i8, i8* %tmp_ret, !dbg !18
  br label %bb1, !dbg !18

bb1:                                              ; preds = %start
  %2 = xor i8 %1, 32, !dbg !18
  store volatile i8 %2, i8* inttoptr (i16 37 to i8*), align 1, !dbg !18
  br label %bb2, !dbg !18

bb2:                                              ; preds = %bb1
  ret void, !dbg !19
}

attributes #0 = { nounwind uwtable "no-frame-pointer-elim"="true" }

!llvm.module.flags = !{!0, !1}
!llvm.dbg.cu = !{!2}

!0 = !{i32 1, !"PIE Level", i32 2}
!1 = !{i32 2, !"Debug Info Version", i32 3}
!2 = distinct !DICompileUnit(language: DW_LANG_Rust, file: !3, producer: "clang LLVM (rustc version 1.18.0-dev (f8982f5c8 2017-04-27))", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4)
!3 = !DIFile(filename: "interrupt", directory: "/home/dylan/projects/builds/rust-lang/avr-rust")
!4 = !{}
!5 = distinct !DISubprogram(name: "main", linkageName: "_ZN9interrupt4mainE", scope: !7, file: !6, line: 87, type: !8, isLocal: false, isDefinition: true, scopeLine: 87, flags: DIFlagPrototyped, isOptimized: false, unit: !2, templateParams: !4, variables: !4)
!6 = !DIFile(filename: "/tmp/interrupt.rs", directory: "/home/dylan/projects/builds/rust-lang/avr-rust")
!7 = !DINamespace(name: "interrupt", scope: null, file: !6, line: 1)
!8 = !DISubroutineType(types: !9)
!9 = !{null}
!10 = !DILocation(line: 89, scope: !5)
!11 = !DILocation(line: 92, scope: !5)
!12 = !DILocation(line: 95, scope: !5)
!13 = !DILocation(line: 98, scope: !5)
!14 = !DILocation(line: 101, scope: !5)
!15 = !{i32 1}
!16 = !DILocation(line: 103, scope: !5)
!17 = distinct !DISubprogram(name: "__vector_11", linkageName: "_ZN9interrupt11__vector_11E", scope: !7, file: !6, line: 108, type: !8, isLocal: false, isDefinition: true, scopeLine: 108, flags: DIFlagPrototyped, isOptimized: false, unit: !2, templateParams: !4, variables: !4)
!18 = !DILocation(line: 109, scope: !17)
!19 = !DILocation(line: 110, scope: !17)

[dylanmckay]

Got a fix for this locally but it breaks a bunch of tests (presumably because the call frame for all functions has now changed).

[dylanmckay]

Fixed in r301887 (EDIT: and in r301893). We previously broke the buildbot (#38, so we could enable FP everywhere).

I will leave the bot red because the 'FP everywhere' thing is temporary and not worth updating dozens of tests for.

Once we revert the 'fp everywhere' patch and come up with a better fix, I will have to go back and fix the tests broken by r301887 (EDIT: and in r301893) itself.

Cherry-picking the patches into our fork.

[dylanmckay]

By the way @gergoerdi, with the commits for this and #38, your interrupt test case (in #38) compiles fine and doesn't give any warnings from simavr.

[dylanmckay]

Cherry picked the fixes from llvm-mirror/llvm@b0cacfc in 577e28d.

[dylanmckay]

I reverted the 'FP everywhere' commit locally so that I could fix all of the tests that r301887 broke. I discovered that r301887 actually regressed normal functions.

I've pushing up another fix, and now the test suite (while still red) is only red because of #38.

[dylanmckay]

The fix (llvm-mirror/llvm@8c15c7b) is now in avr-support