[llvm-bugs] [Bug 27241] New: X86 call frame optimization should be generalized to support 64-bit targets

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=27241

            Bug ID: 27241
           Summary: X86 call frame optimization should be generalized to
                    support 64-bit targets
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: david.l.kreitzer at intel.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

On 64-bit Linux, we should use pushes to store outgoing arguments to the stack
just like we do for 32-bits (subject to profitability checks). For example, in
the calls to f2 below, the last 3 arguments could be passed via push.

---- t.ll ----
target triple = "x86_64-unknown-linux-gnu"

define void @f1() {
entry:
  tail call void @f2(i32 42, i32 43, i32 44, i32 45, i32 46, i32 47, i32 48,
i32 49, i32 50)
  ret void
}

declare void @f2(i32, i32, i32, i32, i32, i32, i32, i32, i32)
--------------

Like this:

---- t.s ----
f1:                                     # @f1
    .cfi_startproc
# BB#0:                                 # %entry
    pushq    %rax
.Ltmp0:
    .cfi_def_cfa_offset 16
    subq    $8, %rsp
.Ltmp1:
    .cfi_adjust_cfa_offset 8
    movl    $42, %edi
    movl    $43, %esi
    movl    $44, %edx
    movl    $45, %ecx
    movl    $46, %r8d
    movl    $47, %r9d
    pushq    $50
.Ltmp2:
    .cfi_adjust_cfa_offset 8
    pushq    $49
.Ltmp3:
    .cfi_adjust_cfa_offset 8
    pushq    $48
.Ltmp4:
    .cfi_adjust_cfa_offset 8
    callq    f2
    addq    $32, %rsp
.Ltmp5:
    .cfi_adjust_cfa_offset -32
    popq    %rax
    retq
-------------

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