[all-commits] [llvm/llvm-project] 2fe315: [X86] TCRETURNmi fix for 32bit platform

[Tong Zhang via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 2fe315162e44084004827e70dcc31c21b1ebd181
      https://github.com/llvm/llvm-project/commit/2fe315162e44084004827e70dcc31c21b1ebd181
  Author: Tong Zhang <ztong0001 at gmail.com>
  Date:   2022-02-09 (Wed, 09 Feb 2022)

  Changed paths:
    M llvm/lib/Target/X86/X86InstrCompiler.td
    A llvm/test/CodeGen/X86/tailcall-3regparm.ll

  Log Message:
  -----------
  [X86] TCRETURNmi fix for 32bit platform

This fix is similar to 3cf3ffce240e("Fix the TCRETURNmi64 bug differently.")

after allocating register for index+base, we will only have one register left

This bug affects linux kernel compilation for x86 target. Error happens when compiling kmod_si476x_core.

clang complains:
    error: ran out of registers during register allocation

The full command is:

clang -Wp,-MMD,drivers/mfd/.si476x-cmd.o.d  -nostdinc -isystem /opt/toolchain/main/lib/clang/14.0.0/include -I./arch/x86/include -I./arch/x86/include/generated  -I./include -I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/compiler-version.h -include ./include/linux/kconfig.h -include ./include/linux/compiler_types.h -D__KERNEL__ -Qunused-arguments -fmacro-prefix-map=./= -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE -Werror=implicit-function-declaration -Werror=implicit-int -Werror=return-type -Wno-format-security -std=gnu89 -no-integrated-as --prefix=/usr/bin/ -Werror=unknown-warning-option -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -fcf-protection=none -m32 -msoft-float -mregparm=3 -freg-struct-return -fno-pic -mstack-alignment=4 -march=atom -mtune=atom -mtune=generic -Wa,-mtune=generic32 -ffreestanding -Wno-sign-compare -fno-asynchronous-unwind-tables -fno-delete-null-pointer-checks -Wno-frame-address -Wno-address-of-packed-member -O2 -Wframe-larger-than=1024 -fno-stack-protector -Wno-format-invalid-specifier -Wno-gnu -mno-global-merge -Wno-unused-but-set-variable -Wno-unused-const-variable -fomit-frame-pointer -ftrivial-auto-var-init=pattern -fno-stack-clash-protection -falign-functions=32 -Wdeclaration-after-statement -Wvla -Wno-pointer-sign -Wno-array-bounds -fno-strict-overflow -fno-stack-check -Werror=date-time -Werror=incompatible-pointer-types -Wno-initializer-overrides -Wno-format -Wno-sign-compare -Wno-format-zero-length -Wno-pointer-to-enum-cast -Wno-tautological-constant-out-of-range-compare     -DKBUILD_MODFILE='"drivers/mfd/si476x-core"' -DKBUILD_BASENAME='"si476x_cmd"' -DKBUILD_MODNAME='"si476x_core"' -D__KBUILD_MODNAME=kmod_si476x_core -c -o drivers/mfd/si476x-cmd.o drivers/mfd/si476x-cmd.c

-------------

LLVM cannot compile the following code for x86 32bit target, the reason is tail call(TCRETURNmi) is using 2 registers for index+base and we want to use more than one registers for passing function args and that is impossible.
This fix is similar to 3cf3ffce240e("Fix the TCRETURNmi64 bug differently.").
We will only use tail call when it is using <=1 registers for passing args.

```
struct BIG_PARM {
	int ver;
};

static struct {
	int (*foo)  (struct BIG_PARM* a, void *b);
	int (*bar)  (struct BIG_PARM* a);
	int (*zoo0) (void);
	int (*zoo1) (void);
	int (*zoo2) (void);
	int (*zoo3) (void);
	int (*zoo4) (void);
} vtable[] = {
	[0] = {
		.foo = (int (*)(struct BIG_PARM* a, void *b))0xdeadbeef,
	},
};

int something(struct BIG_PARM *a, void* b) {
	return vtable[a->ver].foo(a,b);
}

```

```
$ clang -std=gnu89 -m32 -mregparm=3 -mtune=generic -fno-strict-overflow -O2 -c t0.c -o t0.c.o
error: ran out of registers during register allocation
1 error generated.
```

Reviewed By: pengfei

Differential Revision: https://reviews.llvm.org/D118312