[cfe-dev] x86_64-pc-win32 ABI var arg code gen bug? Is the bitcode correct? Or is it the code gen?

[Andrew Fish]

It looks like for x86_64-pc-win32 the compiler does not generate the correct code? It looks like the spill of the argument registers to the 32-byte callers shadow space is not in the bitcode?

I have some code (attached as v.c):

int
ShellPrintHiiEx (
  int                  Col,
  int                  Row,
  const char           *Language,
  const void           *HiiFormatStringId,
  const void           *HiiFormatHandle,
  ...
  )
{
  VA_LIST           Marker;
  int               Value;

  VA_START (Marker, HiiFormatHandle);
  Value = ReturnMarker (Marker);
  VA_END(Marker);
  
  return Value;
}

clang -ccc-host-triple x86_64-pc-win32 -emit-llvm -S  v.c
declare void @llvm.va_start(i8*) nounwind

declare void @llvm.va_end(i8*) nounwind

define i32 @ShellPrintHiiEx(i32 %Col, i32 %Row, i8* %Language, i8* %HiiFormatStringId, i8* %HiiFormatHandle, ...) nounwind {
  %1 = alloca i32, align 4
  %2 = alloca i32, align 4
  %3 = alloca i8*, align 8
  %4 = alloca i8*, align 8
  %5 = alloca i8*, align 8
  %Marker = alloca i8*, align 8
  %Value = alloca i32, align 4
  store i32 %Col, i32* %1, align 4
  store i32 %Row, i32* %2, align 4
  store i8* %Language, i8** %3, align 8
  store i8* %HiiFormatStringId, i8** %4, align 8
  store i8* %HiiFormatHandle, i8** %5, align 8
  %6 = bitcast i8** %Marker to i8*
  call void @llvm.va_start(i8* %6)
  %7 = load i8** %Marker, align 8
  %8 = call i32 @ReturnMarker(i8* %7)
  store i32 %8, i32* %Value, align 4
  %9 = bitcast i8** %Marker to i8*
  call void @llvm.va_end(i8* %9)
  %10 = load i32* %Value, align 4
  ret i32 %10
}

So for x86_64-pc-win32 Col (%rcx), Row (%rdx), Language (%r8), and HiiFormatStringId (%r9) should be spilled to the 32-byte space allocated on the callers stack? Looks like they are being spilled locally?

Does this mean the bitcode needs to be generated differently for x86_64-pc-win32, or does magic occur when code is generated and there is a bug in that chunk of code?


clang -ccc-host-triple x86_64-pc-win32  -S  v.c

	.globl	ShellPrintHiiEx
	.align	16, 0x90
ShellPrintHiiEx:                        # @ShellPrintHiiEx
# BB#0:
	pushq	%rbp
.Ltmp4:
	movq	%rsp, %rbp
.Ltmp5:
	subq	$80, %rsp
.Ltmp6:
	movq	48(%rbp), %rax
	movl	%ecx, -4(%rbp)
	movl	%edx, -8(%rbp)
	movq	%r8, -16(%rbp)
	movq	%r9, -24(%rbp)
	movq	%rax, -32(%rbp)
	leaq	48(%rbp), %rax
	movq	%rax, -40(%rbp)
	movq	%rax, %rcx
	callq	ReturnMarker
	movl	%eax, -44(%rbp)
	addq	$80, %rsp
	popq	%rbp
	ret

Col (%rcx), Row (%rdx), Language (%r8), and HiiFormatStringId (%r9), are spilled to wrong location.

Thanks,

Andrew Fish




cc.exe /FAcs output showing spill to callers stack:

_TEXT	SEGMENT
Value$ = 32
Marker$ = 40
Col$ = 64
Row$ = 72
Language$ = 80
HiiFormatStringId$ = 88
HiiFormatHandle$ = 96
ShellPrintHiiEx PROC NEAR

; 78   : {

$LN3:
  00030	4c 89 4c 24 20	 mov	 QWORD PTR [rsp+32], r9
  00035	4c 89 44 24 18	 mov	 QWORD PTR [rsp+24], r8
  0003a	89 54 24 10	 mov	 DWORD PTR [rsp+16], edx
  0003e	89 4c 24 08	 mov	 DWORD PTR [rsp+8], ecx
  00042	48 83 ec 38	 sub	 rsp, 56			; 00000038H

; 79   :   VA_LIST           Marker;
; 80   :   int               Value;
; 81   : 
; 82   :   VA_START (Marker, HiiFormatHandle);

  00046	48 8d 44 24 68	 lea	 rax, QWORD PTR HiiFormatHandle$[rsp+8]
  0004b	48 89 44 24 28	 mov	 QWORD PTR Marker$[rsp], rax

; 83   :   Value = ReturnMarker (Marker);

  00050	48 8b 4c 24 28	 mov	 rcx, QWORD PTR Marker$[rsp]
  00055	e8 00 00 00 00	 call	 ReturnMarker
  0005a	89 44 24 20	 mov	 DWORD PTR Value$[rsp], eax

; 84   :   VA_END(Marker);

  0005e	48 c7 44 24 28
	00 00 00 00	 mov	 QWORD PTR Marker$[rsp], 0

; 85   :   
; 86   :   return Value;

  00067	8b 44 24 20	 mov	 eax, DWORD PTR Value$[rsp]

; 87   : }


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