[AArch64][GlobalISel] Support lowering musttail calls

Since we now lower most tail calls, it makes sense to support musttail.

Instead of always falling back to SelectionDAG, only fall back when a musttail
call was not able to be emitted as a tail call. Once we can handle most
incoming and outgoing arguments, we can change this to a `report_fatal_error`
like in ISelLowering.

Remove the assert that we don't have varargs and a musttail, and replace it
with a return false. Implementing this requires that we implement
`saveVarArgRegisters` from AArch64ISelLowering, which is an entirely different
patch.

Add GlobalISel lines to vararg-tallcall.ll to make sure that we produce correct
code. Right now we only fall back, but eventually this will be relevant.

Differential Revision: https://reviews.llvm.org/D67681

llvm-svn: 372273

2 files changed, 24 insertions, 6 deletions

diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/call-translator-musttail.ll b/llvm/test/CodeGen/AArch64/GlobalISel/call-translator-musttail.ll
index 7d6ba8489b7..72af098a894 100644
--- a/llvm/test/CodeGen/AArch64/GlobalISel/call-translator-musttail.ll
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/call-translator-musttail.ll
@@ -1,10 +1,13 @@
-; RUN: not llc %s -mtriple aarch64-unknown-unknown -debug-only=aarch64-call-lowering -global-isel -o - 2>&1 | FileCheck %s
+; RUN: not llc %s -mtriple aarch64-apple-darwin -debug-only=aarch64-call-lowering -global-isel -global-isel-abort=2 -o - 2>&1 | FileCheck %s
 ; REQUIRES: asserts
 
-; CHECK: Cannot lower musttail calls yet.
-; CHECK-NEXT: LLVM ERROR: unable to translate instruction: call (in function: foo)
-declare void @must_callee(i8*)
-define void @foo(i32*) {
-  musttail call void @must_callee(i8* null)
+; Verify that we fall back to SelectionDAG, and error out when we can't tail call musttail functions
+; CHECK: ... Cannot tail call externally-defined function with weak linkage for this OS.
+; CHECK-NEXT: Failed to lower musttail call as tail call
+; CHECK-NEXT: warning: Instruction selection used fallback path for caller_weak
+; CHECK-NEXT: LLVM ERROR: failed to perform tail call elimination on a call site marked musttail
+declare extern_weak void @callee_weak()
+define void @caller_weak() {
+  musttail call void @callee_weak()
   ret void
 }
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/call-translator-tail-call.ll b/llvm/test/CodeGen/AArch64/GlobalISel/call-translator-tail-call.ll
index 5be29e04512..78ab27e1039 100644
--- a/llvm/test/CodeGen/AArch64/GlobalISel/call-translator-tail-call.ll
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/call-translator-tail-call.ll
@@ -224,3 +224,18 @@ define hidden swiftcc i64 @swiftself_indirect_tail(i64* swiftself %arg) {
   %tmp2 = tail call swiftcc i64 %tmp1(i64* swiftself %arg)
   ret i64 %tmp2
 }
+
+; Verify that we can tail call musttail callees.
+declare void @must_callee(i8*)
+define void @foo(i32*) {
+  ; COMMON-LABEL: name: foo
+  ; COMMON: bb.1 (%ir-block.1):
+  ; COMMON:   liveins: $x0
+  ; COMMON:   [[COPY:%[0-9]+]]:_(p0) = COPY $x0
+  ; COMMON:   [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 0
+  ; COMMON:   [[INTTOPTR:%[0-9]+]]:_(p0) = G_INTTOPTR [[C]](s64)
+  ; COMMON:   $x0 = COPY [[INTTOPTR]](p0)
+  ; COMMON:   TCRETURNdi @must_callee, 0, csr_aarch64_aapcs, implicit $sp, implicit $x0
+  musttail call void @must_callee(i8* null)
+  ret void
+}