[clang] [llvm] Try to use non-volatile registers for `preserve_none` parameters (PR #88333)
Brandt Bucher via llvm-commits
llvm-commits at lists.llvm.org
Fri Apr 26 16:48:33 PDT 2024
https://github.com/brandtbucher updated https://github.com/llvm/llvm-project/pull/88333
>From f797b695ce38f46563f3724dcffee4005c65c659 Mon Sep 17 00:00:00 2001
From: Brandt Bucher <brandtbucher at microsoft.com>
Date: Wed, 10 Apr 2024 17:03:19 -0700
Subject: [PATCH 1/2] Prefer non-volatile registers for preserve_none
Use non-volatile registers for the first four (six
on Windows) registers used for preserve_none
argument passing. This allows these registers to
stay "pinned" across a chain of tail calls, even
when the body of a preserve_none function contains
other calls.
---
llvm/lib/Target/X86/X86CallingConv.td | 10 ++--
llvm/test/CodeGen/X86/preserve_nonecc_call.ll | 50 +++++++++++++------
.../CodeGen/X86/preserve_nonecc_call_win.ll | 21 ++++++++
3 files changed, 61 insertions(+), 20 deletions(-)
create mode 100644 llvm/test/CodeGen/X86/preserve_nonecc_call_win.ll
diff --git a/llvm/lib/Target/X86/X86CallingConv.td b/llvm/lib/Target/X86/X86CallingConv.td
index 12178bcaf042db..9ec68bfb8e0f7e 100644
--- a/llvm/lib/Target/X86/X86CallingConv.td
+++ b/llvm/lib/Target/X86/X86CallingConv.td
@@ -1063,11 +1063,13 @@ def CC_X86_64_Preserve_None : CallingConv<[
// - R10 'nest' parameter
// - RBX base pointer
// - R16 - R31 these are not available everywhere
- CCIfType<[i32], CCAssignToReg<[EDI, ESI, EDX, ECX, R8D, R9D,
- R11D, R12D, R13D, R14D, R15D, EAX]>>,
+ // Use non-volatile registers first, so functions using this convention can
+ // call "normal" functions without saving and restoring incoming values:
+ CCIfType<[i32], CCAssignToReg<[R12D, R13D, R14D, R15D, EDI, ESI,
+ EDX, ECX, R8D, R9D, R11D, EAX]>>,
- CCIfType<[i64], CCAssignToReg<[RDI, RSI, RDX, RCX, R8, R9,
- R11, R12, R13, R14, R15, RAX]>>,
+ CCIfType<[i64], CCAssignToReg<[R12, R13, R14, R15, RDI, RSI,
+ RDX, RCX, R8, R9, R11, RAX]>>,
// Otherwise it's the same as the regular C calling convention.
CCDelegateTo<CC_X86_64_C>
diff --git a/llvm/test/CodeGen/X86/preserve_nonecc_call.ll b/llvm/test/CodeGen/X86/preserve_nonecc_call.ll
index e4ad056913c5dc..500ebb139811aa 100644
--- a/llvm/test/CodeGen/X86/preserve_nonecc_call.ll
+++ b/llvm/test/CodeGen/X86/preserve_nonecc_call.ll
@@ -27,6 +27,7 @@ define void @caller1(ptr %a) {
; CHECK-NEXT: .cfi_offset %r13, -32
; CHECK-NEXT: .cfi_offset %r14, -24
; CHECK-NEXT: .cfi_offset %r15, -16
+; CHECK-NEXT: movq %rdi, %r12
; CHECK-NEXT: callq callee at PLT
; CHECK-NEXT: popq %rbx
; CHECK-NEXT: .cfi_def_cfa_offset 40
@@ -61,17 +62,17 @@ define preserve_nonecc i64 @callee_with_many_param(i64 %a1, i64 %a2, i64 %a3, i6
; CHECK: # %bb.0:
; CHECK-NEXT: pushq %rax
; CHECK-NEXT: .cfi_def_cfa_offset 16
+; CHECK-NEXT: movq %r13, %r12
+; CHECK-NEXT: movq %r14, %r13
+; CHECK-NEXT: movq %r15, %r14
+; CHECK-NEXT: movq %rdi, %r15
; CHECK-NEXT: movq %rsi, %rdi
; CHECK-NEXT: movq %rdx, %rsi
; CHECK-NEXT: movq %rcx, %rdx
; CHECK-NEXT: movq %r8, %rcx
; CHECK-NEXT: movq %r9, %r8
; CHECK-NEXT: movq %r11, %r9
-; CHECK-NEXT: movq %r12, %r11
-; CHECK-NEXT: movq %r13, %r12
-; CHECK-NEXT: movq %r14, %r13
-; CHECK-NEXT: movq %r15, %r14
-; CHECK-NEXT: movq %rax, %r15
+; CHECK-NEXT: movq %rax, %r11
; CHECK-NEXT: callq callee_with_many_param2 at PLT
; CHECK-NEXT: popq %rcx
; CHECK-NEXT: .cfi_def_cfa_offset 8
@@ -98,17 +99,17 @@ define i64 @caller3() {
; CHECK-NEXT: .cfi_offset %r13, -32
; CHECK-NEXT: .cfi_offset %r14, -24
; CHECK-NEXT: .cfi_offset %r15, -16
-; CHECK-NEXT: movl $1, %edi
-; CHECK-NEXT: movl $2, %esi
-; CHECK-NEXT: movl $3, %edx
-; CHECK-NEXT: movl $4, %ecx
-; CHECK-NEXT: movl $5, %r8d
-; CHECK-NEXT: movl $6, %r9d
-; CHECK-NEXT: movl $7, %r11d
-; CHECK-NEXT: movl $8, %r12d
-; CHECK-NEXT: movl $9, %r13d
-; CHECK-NEXT: movl $10, %r14d
-; CHECK-NEXT: movl $11, %r15d
+; CHECK-NEXT: movl $1, %r12d
+; CHECK-NEXT: movl $2, %r13d
+; CHECK-NEXT: movl $3, %r14d
+; CHECK-NEXT: movl $4, %r15d
+; CHECK-NEXT: movl $5, %edi
+; CHECK-NEXT: movl $6, %esi
+; CHECK-NEXT: movl $7, %edx
+; CHECK-NEXT: movl $8, %ecx
+; CHECK-NEXT: movl $9, %r8d
+; CHECK-NEXT: movl $10, %r9d
+; CHECK-NEXT: movl $11, %r11d
; CHECK-NEXT: movl $12, %eax
; CHECK-NEXT: callq callee_with_many_param at PLT
; CHECK-NEXT: popq %rbx
@@ -125,3 +126,20 @@ define i64 @caller3() {
%ret = call preserve_nonecc i64 @callee_with_many_param(i64 1, i64 2, i64 3, i64 4, i64 5, i64 6, i64 7, i64 8, i64 9, i64 10, i64 11, i64 12)
ret i64 %ret
}
+
+; Non-volatile registers are used to pass the first few parameters.
+declare void @boring()
+declare preserve_nonecc void @continuation(ptr, ptr, ptr, ptr)
+define preserve_nonecc void @entry(ptr %r12, ptr %r13, ptr %r14, ptr %r15) {
+; CHECK-LABEL: entry:
+; CHECK: # %bb.0:
+; CHECK-NEXT: pushq %rax
+; CHECK-NEXT: .cfi_def_cfa_offset 16
+; CHECK-NEXT: callq boring at PLT
+; CHECK-NEXT: popq %rax
+; CHECK-NEXT: .cfi_def_cfa_offset 8
+; CHECK-NEXT: jmp continuation at PLT # TAILCALL
+ call void @boring()
+ musttail call preserve_nonecc void @continuation(ptr %r12, ptr %r13, ptr %r14, ptr %r15)
+ ret void
+}
diff --git a/llvm/test/CodeGen/X86/preserve_nonecc_call_win.ll b/llvm/test/CodeGen/X86/preserve_nonecc_call_win.ll
new file mode 100644
index 00000000000000..232ac345057825
--- /dev/null
+++ b/llvm/test/CodeGen/X86/preserve_nonecc_call_win.ll
@@ -0,0 +1,21 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc -mtriple=x86_64-pc-windows-msvc -mcpu=corei7 < %s | FileCheck %s
+
+; Non-volatile registers are used to pass the first few parameters.
+declare void @boring()
+declare preserve_nonecc void @continuation(ptr, ptr, ptr, ptr, ptr, ptr)
+define preserve_nonecc void @entry(ptr %r12, ptr %r13, ptr %r14, ptr %r15, ptr %rdi, ptr %rsi) {
+; CHECK-LABEL: entry:
+; CHECK: # %bb.0:
+; CHECK-NEXT: subq $40, %rsp
+; CHECK-NEXT: .seh_stackalloc 40
+; CHECK-NEXT: .seh_endprologue
+; CHECK-NEXT: callq boring
+; CHECK-NEXT: nop
+; CHECK-NEXT: addq $40, %rsp
+; CHECK-NEXT: jmp continuation # TAILCALL
+; CHECK-NEXT: .seh_endproc
+ call void @boring()
+ musttail call preserve_nonecc void @continuation(ptr %r12, ptr %r13, ptr %r14, ptr %r15, ptr %rdi, ptr %rsi)
+ ret void
+}
>From 22868d373b85da911131a540227f96227fb7f4e1 Mon Sep 17 00:00:00 2001
From: Brandt Bucher <brandtbucher at microsoft.com>
Date: Fri, 26 Apr 2024 16:48:13 -0700
Subject: [PATCH 2/2] Note that preserve_none's ABI is unstable
---
clang/include/clang/Basic/AttrDocs.td | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index 0ca4ea377fc36a..264b0299f0d1a5 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -5641,11 +5641,12 @@ The ``preserve_none`` calling convention tries to preserve as few general
registers as possible. So all general registers are caller saved registers. It
also uses more general registers to pass arguments. This attribute doesn't
impact floating-point registers (XMMs/YMMs). Floating-point registers still
-follow the c calling convention.
+follow the c calling convention. ``preserve_none``'s ABI is still unstable, and
+may be changed in the future.
- Only RSP and RBP are preserved by callee.
-- Register RDI, RSI, RDX, RCX, R8, R9, R11, R12, R13, R14, R15 and RAX now can
+- Register R12, R13, R14, R15, RDI, RSI, RDX, RCX, R8, R9, R11, and RAX now can
be used to pass function arguments.
}];
}
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