[llvm] [AArch64][SME] Don't use glue for call lowering's SMSTART. (PR #68630)

[Amara Emerson via llvm-commits]

https://github.com/aemerson created https://github.com/llvm/llvm-project/pull/68630

The glue operand causes the SMSTART instruction to have implicit register definitions added by InstrEmitter, since the actual call instruction uses those physregs.

I've been working on LLVM for over a decade now, and I've still yet to understand what Glue is, so I'm not sure if this change is correct.

>From 2f50512ca850771ba74b6260c6d93b17e987689e Mon Sep 17 00:00:00 2001
From: Amara Emerson <amara at apple.com>
Date: Mon, 9 Oct 2023 13:56:46 -0700
Subject: [PATCH] [AArch64][SME] Don't use glue for call lowering's SMSTART.

The glue operand causes the SMSTART instruction to have implicit register
definitions added by InstrEmitter, since the actual call instruction uses
those physregs.
---
 llvm/lib/Target/AArch64/AArch64ISelLowering.cpp      |  5 ++---
 llvm/test/CodeGen/AArch64/sme-streaming-interface.ll | 12 ++++--------
 2 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index 9cda43e58d27a43..9ecc53f3ee4e8b2 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -7687,14 +7687,13 @@ AArch64TargetLowering::LowerCall(CallLoweringInfo &CLI,
   if (!MemOpChains.empty())
     Chain = DAG.getNode(ISD::TokenFactor, DL, MVT::Other, MemOpChains);
 
-  SDValue InGlue;
   if (RequiresSMChange) {
     SDValue NewChain = changeStreamingMode(DAG, DL, *RequiresSMChange, Chain,
-                                           InGlue, PStateSM, true);
+                                           SDValue(), PStateSM, true);
     Chain = NewChain.getValue(0);
-    InGlue = NewChain.getValue(1);
   }
 
+  SDValue InGlue;
   // Build a sequence of copy-to-reg nodes chained together with token chain
   // and flag operands which copy the outgoing args into the appropriate regs.
   for (auto &RegToPass : RegsToPass) {
diff --git a/llvm/test/CodeGen/AArch64/sme-streaming-interface.ll b/llvm/test/CodeGen/AArch64/sme-streaming-interface.ll
index 102ed896ce7b3e8..46b7241076a1bd3 100644
--- a/llvm/test/CodeGen/AArch64/sme-streaming-interface.ll
+++ b/llvm/test/CodeGen/AArch64/sme-streaming-interface.ll
@@ -368,15 +368,11 @@ define i8 @call_to_non_streaming_pass_sve_objects(ptr nocapture noundef readnone
 ; CHECK-NEXT:    stp d9, d8, [sp, #48] // 16-byte Folded Spill
 ; CHECK-NEXT:    stp x29, x30, [sp, #64] // 16-byte Folded Spill
 ; CHECK-NEXT:    addvl sp, sp, #-3
-; CHECK-NEXT:    rdsvl x8, #1
-; CHECK-NEXT:    addvl x9, sp, #2
-; CHECK-NEXT:    addvl x10, sp, #1
-; CHECK-NEXT:    mov x11, sp
+; CHECK-NEXT:    rdsvl x3, #1
 ; CHECK-NEXT:    smstop sm
-; CHECK-NEXT:    mov x0, x9
-; CHECK-NEXT:    mov x1, x10
-; CHECK-NEXT:    mov x2, x11
-; CHECK-NEXT:    mov x3, x8
+; CHECK-NEXT:    addvl x0, sp, #2
+; CHECK-NEXT:    addvl x1, sp, #1
+; CHECK-NEXT:    mov x2, sp
 ; CHECK-NEXT:    bl foo
 ; CHECK-NEXT:    smstart sm
 ; CHECK-NEXT:    ptrue p0.b