• d-bugmail puremagic.com (119/119) Feb 22 2020 https://issues.dlang.org/show_bug.cgi?id=20594

d-bugmail puremagic.com writes:

https://issues.dlang.org/show_bug.cgi?id=20594

          Issue ID: 20594
           Summary: [GCC ASM] Should the asm { } syntax be modernized for
                    D2?
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: ibuclaw gdcproject.org

The current syntax of the `asm { }` body follows the gcc extended style as
documented in https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html

This has been the case in gdc long before D1 v1.001 was released.

This has been argued that it rather counters what is considered tasteful D
style code.

Consider the existing style:

asm pure nothrow  nogc {
    "cmoveq %1, %2, %[result]"    // insn
    : [result] "=r" (result)      // outputs
    : "r" (test), "r" (newvalue), // inputs
      "[result]" (oldvalue)
    : "memory";                   // clobbers
}


Then consider what that would look like if output/inputs were a hash, and
clobbers an array:

asm pure nothrow  nogc {
    "cmoveq %1, %2, %[result]"    // insn
    : [result = "=r": result]     // outputs
    : ["r": test, "r": newvalue,  // inputs
       "[result]": oldvalue]
    : ["memory"];                 // clobbers
}

Then going one further and replacing the colons with commas.

asm pure nothrow  nogc {
    "cmoveq %1, %2, %[result]",   // insn
    [result = "=r": result],      // outputs
    ["r": test, "r": newvalue,    // inputs
     "[result]": oldvalue],
    ["memory"];                   // clobbers
}

---

Some examples of what this might look like in other cases:

asm nothrow  nogc {
    "xchg %h0, %b0", ["+a": num];
}

asm nothrow  nogc {
    "mtfsf 255,%1", ["=X": sum], ["f": fpenv];
}

asm nothrow  nogc {
    "", [], [], ["memory"];  // volatile barrier.
}

asm pure nothrow  nogc {
    "bsfl %1,%0", ["=r": dwRes], ["r": dwSomeValue], ["cc"];
}

asm nothrow  nogc {
    "rdtsc\n\t"
    "shl $32, %%rdx\n\t"
    "or %%rdx, %0",
    ["=a": msr], [], ["rdx"];
}

asm nothrow  nogc {
    /* lots of asm here */
    "#n=%1 ap=%8=%12 lda=%13 x=%7=%10 y=%0=%2 alpha=%9 o16=%11\n"
    "#a0=%3 a1=%4 a2=%5 a3=%6",
    [   // outputs
        "+m": *cast(double[10]*) y,
        "+&r": n,  // 1
        "+b": y,   // 2
        "=b": a0,  // 3
        "=&b": a1, // 4
        "=&b": a2, // 5
        "=&b": a3, // 6
    ],
    [   // inputs
        "m": *cast(double[10]*) x,
        "m": *cast(double*) ap,
        "d": alpha, // 9
        "r": x,     // 10
        "b": 16,    // 11
        "3": ap,    // 12
        "4": lda,   // 13
    ],
    [  // clobbers
       "cr0",
       "vs32","vs33","vs34","vs35","vs36","vs37",
       "vs40","vs41","vs42","vs43","vs44","vs45","vs46","vs47"
    ];
}

int frob(int x)
{
    int y;
    asm {
        "frob %%r5, %1; jc %l[error]; mov (%2), %%r5",
        [/* No outputs. */],
        ["r": x, "r": &y],
        ["r5", "memory"],
        [Lerror];
    }
    return y;
Lerror:
    return -1;
}

int main()
{
    int iInt = 1;
top:
    asm nothrow  nogc {
        "some assembler instructions here",
        [/* No outputs. */],
        ["q": iInt, "X": char.sizeof + 1, "i": 42],
        [/* No clobbers. */],
        [top];
    }
}

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