[X86] Don't use rbp when it's reserved

[brandtbucher]

This fixes the x86 backend to properly reserve rbp when the frame-pointer=reserved option is used. Currently, this option is ignored.

Disassembly of the new test case before:

pushq %rbp
pushq %rbx
pushq %rax
movl %esi, %ebx
movl %edi, %ebp
callq bar@PLT
movl %ebp, %edi
movl %ebx, %esi
callq bar@PLT
addq $8, %rsp
popq %rbx
popq %rbp
retq

...and after (r14 is used as scratch space in place of rbp):

pushq %r14
pushq %rbx
pushq %rax
movl %esi, %ebx
movl %edi, %r14d
callq bar@PLT
movl %r14d, %edi
movl %ebx, %esi
callq bar@PLT
addq $8, %rsp
popq %rbx
popq %r14
retq

Fixes #117178.

[llvmbot]

@llvm/pr-subscribers-backend-x86

Author: Brandt Bucher (brandtbucher)

Changes

This fixes the x86 backend to properly reserve rbp when the frame-pointer=reserved option is used. Currently, this option is ignored.

Disassembly of the new test case before:

pushq %rbp
pushq %rbx
pushq %rax
movl %esi, %ebx
movl %edi, %ebp
callq bar@<!-- -->PLT
movl %ebp, %edi
movl %ebx, %esi
callq bar@<!-- -->PLT
addq $8, %rsp
popq %rbx
popq %rbp
retq

...and after (r14 is used as scratch space in place of rbp):

pushq %r14
pushq %rbx
pushq %rax
movl %esi, %ebx
movl %edi, %r14d
callq bar@<!-- -->PLT
movl %r14d, %edi
movl %ebx, %esi
callq bar@<!-- -->PLT
addq $8, %rsp
popq %rbx
popq %r14
retq

Fixes #117178.

---

Full diff: https://github.com/llvm/llvm-project/pull/146638.diff

2 Files Affected:

• (modified) llvm/lib/Target/X86/X86RegisterInfo.cpp (+1-1)
• (added) llvm/test/CodeGen/X86/frame-pointer-reserved.ll (+25)

diff --git a/llvm/lib/Target/X86/X86RegisterInfo.cpp b/llvm/lib/Target/X86/X86RegisterInfo.cpp
index 9adac067aace8..83b11eede829e 100644
--- a/llvm/lib/Target/X86/X86RegisterInfo.cpp
+++ b/llvm/lib/Target/X86/X86RegisterInfo.cpp
@@ -562,7 +562,7 @@ BitVector X86RegisterInfo::getReservedRegs(const MachineFunction &MF) const {
     Reserved.set(SubReg);
 
   // Set the frame-pointer register and its aliases as reserved if needed.
-  if (TFI->hasFP(MF)) {
+  if (TFI->hasFP(MF) || MF.getTarget().Options.FramePointerIsReserved(MF)) {
     if (MF.getInfo<X86MachineFunctionInfo>()->getFPClobberedByInvoke())
       MF.getContext().reportError(
           SMLoc(),
diff --git a/llvm/test/CodeGen/X86/frame-pointer-reserved.ll b/llvm/test/CodeGen/X86/frame-pointer-reserved.ll
new file mode 100644
index 0000000000000..bf5887fe50508
--- /dev/null
+++ b/llvm/test/CodeGen/X86/frame-pointer-reserved.ll
@@ -0,0 +1,25 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown | FileCheck %s
+
+declare void @bar(i32, i32)
+
+define void @foo(i32 %0, i32 %1) nounwind "frame-pointer"="reserved" {
+; CHECK-LABEL: foo:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    pushq %r14
+; CHECK-NEXT:    pushq %rbx
+; CHECK-NEXT:    pushq %rax
+; CHECK-NEXT:    movl %esi, %ebx
+; CHECK-NEXT:    movl %edi, %r14d
+; CHECK-NEXT:    callq bar@PLT
+; CHECK-NEXT:    movl %r14d, %edi
+; CHECK-NEXT:    movl %ebx, %esi
+; CHECK-NEXT:    callq bar@PLT
+; CHECK-NEXT:    addq $8, %rsp
+; CHECK-NEXT:    popq %rbx
+; CHECK-NEXT:    popq %r14
+; CHECK-NEXT:    retq
+  call void @bar(i32 %0, i32 %1)
+  call void @bar(i32 %0, i32 %1)
+  ret void
+}

[phoebewang]

LGTM.

[llvm-ci]

LLVM Buildbot has detected a new failure on builder flang-arm64-windows-msvc running on linaro-armv8-windows-msvc-01 while building llvm at step 7 "test-build-unified-tree-check-flang".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/207/builds/3511

Here is the relevant piece of the build log for the reference

Step 7 (test-build-unified-tree-check-flang) failure: test (failure)
******************** TEST 'Flang :: Parser/OpenMP/declare-reduction-operator.f90' FAILED ********************
Exit Code: 2

Command Output (stdout):
--
# RUN: at line 1
c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe -fc1 -fdebug-unparse -fopenmp C:\Users\tcwg\llvm-worker\flang-arm64-windows-msvc\llvm-project\flang\test\Parser\OpenMP\declare-reduction-operator.f90 | c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\filecheck.exe --ignore-case C:\Users\tcwg\llvm-worker\flang-arm64-windows-msvc\llvm-project\flang\test\Parser\OpenMP\declare-reduction-operator.f90
# executed command: 'c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe' -fc1 -fdebug-unparse -fopenmp 'C:\Users\tcwg\llvm-worker\flang-arm64-windows-msvc\llvm-project\flang\test\Parser\OpenMP\declare-reduction-operator.f90'
# .---command stderr------------
# | PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
# | Stack dump:
# | 0.	Program arguments: c:\\users\\tcwg\\llvm-worker\\flang-arm64-windows-msvc\\build\\bin\\flang.exe -fc1 -fdebug-unparse -fopenmp C:\\Users\\tcwg\\llvm-worker\\flang-arm64-windows-msvc\\llvm-project\\flang\\test\\Parser\\OpenMP\\declare-reduction-operator.f90
# | Exception Code: 0xC0000005
# |  #0 0x00007ff7e1472c7c (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0x1a92c7c)
# |  #1 0x00007ff7e1470964 (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0x1a90964)
# |  #2 0x00007ff7e146e7f8 (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0x1a8e7f8)
# |  #3 0x00007ff7e147450c (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0x1a9450c)
# |  #4 0x00007ff7e146e360 (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0x1a8e360)
# |  #5 0x00007ff7e028c808 (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0x8ac808)
# |  #6 0x00007ff7e02d5c68 (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0x8f5c68)
# |  #7 0x00007ff7e037eb24 (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0x99eb24)
# |  #8 0x00007ff7e02d50a4 (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0x8f50a4)
# |  #9 0x00007ff7dfa78ac8 (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0x98ac8)
# | #10 0x00007ff7dfa8ea90 (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0xaea90)
# | #11 0x00007ff7df9e34e8 (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0x34e8)
# | #12 0x00007ff7df9e20a4 (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0x20a4)
# | #13 0x00007ff7e46a0db8 mlir::detail::FallbackTypeIDResolver::registerImplicitTypeID(class llvm::StringRef) (c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\flang.exe+0x4cc0db8)
# | #14 0x225ffff7e46a0e54
# `-----------------------------
# error: command failed with exit status: 0xc0000005
# executed command: 'c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\filecheck.exe' --ignore-case 'C:\Users\tcwg\llvm-worker\flang-arm64-windows-msvc\llvm-project\flang\test\Parser\OpenMP\declare-reduction-operator.f90'
# .---command stderr------------
# | FileCheck error: '<stdin>' is empty.
# | FileCheck command line:  c:\users\tcwg\llvm-worker\flang-arm64-windows-msvc\build\bin\filecheck.exe --ignore-case C:\Users\tcwg\llvm-worker\flang-arm64-windows-msvc\llvm-project\flang\test\Parser\OpenMP\declare-reduction-operator.f90
# `-----------------------------
# error: command failed with exit status: 2

--

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