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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

<details>
<summary>Changes</summary>

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.

---
Full diff: https://github.com/llvm/llvm-project/pull/68630.diff


2 Files Affected:

- (modified) llvm/lib/Target/AArch64/AArch64ISelLowering.cpp (+2-3) 
- (modified) llvm/test/CodeGen/AArch64/sme-streaming-interface.ll (+4-8) 


``````````diff
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

``````````

</details>


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