[llvm] [clang] New calling convention preserve_none (PR #76868)

[David Li via cfe-commits]

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@@ -0,0 +1,131 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc -mtriple=x86_64-unknown-unknown -mcpu=corei7 < %s | FileCheck %s
+
+; This test checks various function call behaviors between preserve_none and
+; normal calling conventions.
+
+declare preserve_nonecc void @callee(ptr)
+
+; Normal caller calls preserve_none callee. Will not generated tail call because
+; of incompatible calling convention. Callee saved registers are saved/restored
+; around the call.
+define void @caller1(ptr %a) {
+; CHECK-LABEL: caller1:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    pushq %r15
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    pushq %r14
+; CHECK-NEXT:    .cfi_def_cfa_offset 24
+; CHECK-NEXT:    pushq %r13
+; CHECK-NEXT:    .cfi_def_cfa_offset 32
+; CHECK-NEXT:    pushq %r12
+; CHECK-NEXT:    .cfi_def_cfa_offset 40
+; CHECK-NEXT:    pushq %rbx
+; CHECK-NEXT:    .cfi_def_cfa_offset 48
+; CHECK-NEXT:    .cfi_offset %rbx, -48
+; CHECK-NEXT:    .cfi_offset %r12, -40
+; CHECK-NEXT:    .cfi_offset %r13, -32
+; CHECK-NEXT:    .cfi_offset %r14, -24
+; CHECK-NEXT:    .cfi_offset %r15, -16
+; CHECK-NEXT:    callq callee at PLT
+; CHECK-NEXT:    popq %rbx
+; CHECK-NEXT:    .cfi_def_cfa_offset 40
+; CHECK-NEXT:    popq %r12
+; CHECK-NEXT:    .cfi_def_cfa_offset 32
+; CHECK-NEXT:    popq %r13
+; CHECK-NEXT:    .cfi_def_cfa_offset 24
+; CHECK-NEXT:    popq %r14
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    popq %r15
+; CHECK-NEXT:    .cfi_def_cfa_offset 8
+; CHECK-NEXT:    retq
+  tail call preserve_nonecc void @callee(ptr %a)
+  ret void
+}
+
+; Preserve_none caller calls preserve_none callee. Same function body.
+; The tail call is preserved. No registers are saved/restored around the call.
+; Actually a simple jmp instruction is generated.
+define preserve_nonecc void @caller2(ptr %a) {
+; CHECK-LABEL: caller2:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    jmp callee at PLT # TAILCALL
+  tail call preserve_nonecc void @callee(ptr %a)
+  ret void
+}
+
+; Preserve_none function can use more registers to pass parameters.
+define preserve_nonecc i64 @callee_with_many_param(i64 %a1, i64 %a2, i64 %a3, i64 %a4, i64 %a5, i64 %a6, i64 %a7, i64 %a8, i64 %a9, i64 %a10, i64 %a11, i64 %a12) {
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david-xl wrote:

or better yet, pass the arguments in order to (tail)call to another preserve_none callee.

https://github.com/llvm/llvm-project/pull/76868