• d-bugmail puremagic.com (32/32) Oct 25 2021 https://issues.dlang.org/show_bug.cgi?id=22438

d-bugmail puremagic.com writes:

https://issues.dlang.org/show_bug.cgi?id=22438

          Issue ID: 22438
           Summary: OPpair codegen fails with mTYxmmgpr and mTYgprxmm
           Product: D
           Version: D2
          Hardware: x86_64
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: bugzilla digitalmars.com

The trouble comes about with the following:

    struct S { int x; double d; }
    S foo(int x, double d) { return S(x, d); }

The SROA optimization replaces the temp struct created by S(x, d) with two
variables. The two variables get combined using OPpair for the return value in
registers RAX and XMM0.

cdpair() can't handle this, so the code generator asks for register pair AX,DX,
intending to fix up the result later in the BCretexp section of
outblkexitcode(). cdpair() obligingly asks loaddata() to load `d` into DX.

This winds up calling loadea() with a MOV opcode 0x8B, which is for GP
registers only. But meantime, d is passed in XMM0. getlvalue() sets the EA bits
for XMM0, but the opcode is 0x8B, so the following code gets generated:

    8B D0    mov RDX,RAX

instead of:

    mov RDX,XMM0

A proper fix is to have outblkexitcode() handle the mTYxmmgpr and mTYgprxmm
kludge cases directly instead of using OPpair.

In the meantime, I'm disabling SROA when they result in a mixed XMM/GPR pair.

--