A test file I was using while trying to fix https://github.com/llvm/llvm-project/issues/20571. It tries to forcibly cause register exhaustion by using inline asm which clobbers all GPRs. In these cases, "rm" contrained operands should fall back to "m" rather than fail to compile.

all_targets.c

// -Wno-asm-operand-widths
// void input_pressure(int x) {
//     // asm ("# %0"::"m"(x):"r0","r1","r2","r3","r12","lr","r4","r5","r6","r7","r8","r9","r10","r11");
//   asm (""::"m"(x));
// }

struct foo {
  long a, b, c, d, e;
};
int zzz (struct foo my_foo) {
// void zzz (struct foo my_foo) {
  // for i in $(seq 0 31); do echo -n "\"r$i\","; done
#ifdef __hexagon__
  asm ("# %0"::"rm"(my_foo.b):"r0","r1","r2","r3","r4","r5","r6","r7","r8","r9","r12","r13","r14","r15","r28","r10","r11","r16","r17","r18","r19","r20","r21","r22","r23","r24","r25","r26","r27");
#endif
#ifdef __x86_64__
  // int x = 42;
  // asm ("# %0"::"m"(x));
  asm ("# %0 %1"::"rm"(my_foo.b),"rm"(my_foo.d):"ax","cx","dx","si","di","r8","r9","r10","r11","bx","bp","r14","r15","r12","r13");
  asm ("# %0 %1":"=rm"(my_foo.b),"=rm"(my_foo.d)::"ax","cx","dx","si","di","r8","r9","r10","r11","bx","bp","r14","r15","r12","r13");
  asm ("# %0 %1":"+rm"(my_foo.b),"+rm"(my_foo.d)::"ax","cx","dx","si","di","r8","r9","r10","r11","bx","bp","r14","r15","r12","r13");
  // return my_foo.d;
  asm ("# %0"::"rm"(my_foo.b));
  asm ("# %0 %1"::"rm"(my_foo.b), "r"(my_foo.d));
  asm ("# %0":"=rm"(my_foo.b));
  asm ("# %0":"+rm"(my_foo.b));
  // asm volatile ("# %0":"=r"(my_foo.b):"0"(my_foo.b));
#endif
#ifdef __i386__
  asm ("# %0"::"rm"(my_foo.b):"ax","cx","dx","si","di","bx","bp");
  asm ("# %0":"=rm"(my_foo.b)::"ax","cx","dx","si","di","bx","bp");
  asm ("# %0":"+rm"(my_foo.b)::"ax","cx","dx","si","di","bx","bp");
#endif
#ifdef __lanai__
  asm (""::"rm"(my_foo.b):"r0","r1","r2","r3","r4","r5","r6","r7","r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18","r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29","r30","r31");
#endif
#ifdef __NVPTX__
  // asm ("# %0 "::"rm"(my_foo.b):"r1");
#endif
// TODO: something fishy is going on for ARM.
#ifdef __arm__
  // int x = 42;
  // asm ("# %0"::"m"(x));
  // asm ("# %0"::"rm"(my_foo.b):"r0","r1","r2","r3","r12","lr","r4","r5","r6","r7","r8","r9","r10","r11");
  asm ("# %0 %1"::"rm"(my_foo.b),"rm"(my_foo.d):"r0","r1","r2","r3","r12","lr","r4","r5","r6","r7","r8","r9","r10","r11");
#endif
#ifdef __aarch64__
  // int x = 42;
  // asm ("# %0"::"m"(x));
  asm ("# %0 %1"::"rm"(my_foo.b),"rm"(my_foo.d):"x8","x9","x10","x11","x12","x13","x14","x15","x16","x17","x18","x0","x1","x2","x3","x4","x5","x6","x7","x19","x20","x21","x22","x23","x24","x25","x26","x27","x28","x29","x30");
  asm ("# %0 %1":"=rm"(my_foo.b),"=rm"(my_foo.d)::"x8","x9","x10","x11","x12","x13","x14","x15","x16","x17","x18","x0","x1","x2","x3","x4","x5","x6","x7","x19","x20","x21","x22","x23","x24","x25","x26","x27","x28","x29","x30");
  asm ("# %0 %1":"+rm"(my_foo.b),"+rm"(my_foo.d)::"x8","x9","x10","x11","x12","x13","x14","x15","x16","x17","x18","x0","x1","x2","x3","x4","x5","x6","x7","x19","x20","x21","x22","x23","x24","x25","x26","x27","x28","x29","x30");
  asm ("# %0"::"rm"(my_foo.b));
  asm ("# %0 %1"::"rm"(my_foo.b), "r"(my_foo.d));
  asm ("# %0":"=rm"(my_foo.b));
  asm ("# %0":"+rm"(my_foo.b));
  // asm ("# %0"::"rm"(my_foo.b):"x8","x9","x10","x11","x12","x13","x14","x15","x16","x17","x18","x0","x1","x2","x3","x4","x5","x6","x7","x19","x20","x21","x22","x23","x24","x25","x26","x27","x28","x29","x30");
  // asm ("# %0"::"mr"(my_foo.b):"x8","x9","x10","x11","x12","x13","x14","x15","x16","x17","x18","x0","x1","x2","x3","x4","x5","x6","x7","x19","x20","x21","x22","x23","x24","x25","x26","x27","x28","x29","x30");
#endif
#ifdef __powerpc64__
  // TODO: only long works, not int
  asm ("# %0 %1"::"rm"(my_foo.b),"rm"(my_foo.d):"r4","r5","r6","r7","r8","r9","r10","r11","r12","r0","r30","r29","r28","r27","r26","r25","r24","r23","r22","r21","r20","r19","r18","r17","r16","r15","r14","r31","r3");
  // long x = 42;
  // asm ("# %0"::"m"(x));
#endif
#ifdef __riscv
  // int x = 42;
  // asm ("# %0"::"m"(x));
  asm ("# %0 %1"::"rm"(my_foo.b), "rm"(my_foo.d):"a1","a2","a3","a4","a5","a6","a7","t0","t1","t2","t3","t4","t5","t6","s0","s1","s2","s3","s4","s5","s6","s7","s8","s9","s10","s11","ra");
#endif
  return my_foo.a;
}

test_cases.ll

; Generate test cases with:
; $ llc -mtriple=i686 test_cases.ll -stop-after={greedy|virtregrewriter} -o -
;define void @input_no_pressure (i32 inreg %x) nounwind {
;  call void asm "# $0", "rm"(i32 %x)
;  ret void
;}
;
;define i32 @output_no_pressure () nounwind {
;  %1 = call i32 asm "# $0", "=rm"()
;  ret i32 %1
;}
;
;define void @input_pressure (i32 inreg %x) nounwind {
;  ; call void asm "", "rm,~{bx},~{cx},~{dx},~{si},~{di},~{bp},~{memory}"(i32 %x)
;  call void asm "# $0", "rm,~{ax},~{bx},~{cx},~{dx},~{si},~{di},~{bp}"(i32 %x)
;  ret void
;}

; define i32 @output_pressure0 () nounwind {
;   %1 = call i32 asm "# $0", "=rm,~{ax},~{bx},~{cx},~{dx},~{si},~{di},~{bp}"()
;   ret i32 %1
; }

;; TODO: clang generates code more like:
;; CodeGenFunction::EmitAsmStmt clang/lib/CodeGen/CGStmt.cpp +2423

;define i32 @output_pressure () nounwind {
;  %x = alloca i32, align 4
;  call void asm "# $0", "=*rm,~{ax},~{bx},~{cx},~{dx},~{si},~{di},~{bp}"(ptr nonnull elementtype(i32) %x)
;  %1 = load i32, ptr %x, align 4
;  ret i32 %1
;}

; define i32 @inout_no_pressure (i32 inreg %x) nounwind {
;   %1 = call i32 asm "# $0", "=rm,0"(i32 %x)
;   ret i32 %1
; }
; define i32 @inout_pressure (i32 inreg %x) nounwind {
;   %1 = call i32 asm "# $0 $1", "=rm,0,~{ax},~{bx},~{cx},~{dx},~{si},~{di},~{bp}"(i32 %x)
;   ret i32 %1
; }

; asm goto

;define void @input_no_pressure_goto (i32 inreg %x) nounwind {
;  callbr void asm "# $0 $1", "rm,!i"(i32 %x)
;  to label %ft [label %ij]
;ft:
;  br label %ij
;ij:
;  ret void
;}
;
;define i32 @output_no_pressure_goto () nounwind {
;  %1 = callbr i32 asm "# $0 $1", "=rm,!i"()
;  to label %ft [label %ij]
;ft:
;  %2 = add nsw i32 %1, 1
;  ret i32 %2
;ij:
;  ret i32 %1
;}
;

define void @input_pressure_goto (i32 inreg %x) nounwind {
  ; call void asm "", "rm,~{bx},~{cx},~{dx},~{si},~{di},~{bp},~{memory}"(i32 %x)
  callbr void asm "# $0 $1", "rm,!i,~{ax},~{bx},~{cx},~{dx},~{si},~{di},~{bp}"(i32 %x)
  to label %ft [label %ij]
ft:
  br label %ij
ij:
  ret void
}

;define i32 @output_pressure0_goto () nounwind {
;   %1 = callbr i32 asm "# $0 $1", "=rm,!i,~{ax},~{bx},~{cx},~{dx},~{si},~{di},~{bp}"()
;   to label %ft [label %ij]
;ft:
;  ret i32 %1
;ij:
;  ret i32 %1
; }

;define i32 @output_pressure_goto () nounwind {
;  %x = alloca i32, align 4
;  callbr void asm "# $0 $1", "=*rm,!i,~{ax},~{bx},~{cx},~{dx},~{si},~{di},~{bp}"(ptr nonnull elementtype(i32) %x)
;  to label %ft [label %ft]
;ft:
;  %1 = load i32, ptr %x, align 4
;  ret i32 %1
;}

; define i32 @inout_no_pressure_goto (i32 inreg %x) nounwind {
;   %1 = callbr i32 asm "# $0 $1", "=rm,!i,0"(i32 %x)
;   to label %ft [label %ft]
;ft:
;   ret i32 %1
; }
 ; TODO: greedy is not spilling this correctly!
; define i32 @inout_pressure_goto (i32 inreg %x) nounwind {
;   %1 = callbr i32 asm "# $0 $1 $2", "=rm,0,!i,~{ax},~{bx},~{cx},~{dx},~{si},~{di},~{bp}"(i32 %x)
;   to label %ft [label %ft]
;ft:
;   ret i32 %1
; }

define void @foo(i32 %x) nounwind {
  call void asm "# $0", "rm,~{eax},~{bx},~{cx},~{dx},~{si},~{di},~{bp}"(i32 %x)
  ret void
}