[llvm] [AMDGPU] In instruction selector, allow copy from physical reg to s1 (PR #96157)

[Jun Wang via llvm-commits]

https://github.com/jwanggit86 created https://github.com/llvm/llvm-project/pull/96157

In planned calling convention update, i1 arguments/returns are assigned to SGPRs without being promoted to i32. We need to update the instruction selector to allow copy from physical reg to s1 destination.

>From 68a0704dc39dfdc37a8fa8baa14078ca04e8c767 Mon Sep 17 00:00:00 2001
From: Jun Wang <jun.wang7 at amd.com>
Date: Thu, 20 Jun 2024 05:12:23 -0500
Subject: [PATCH] [AMDGPU] In instruction selector, allow copy from physical
 reg to s1

In planned calling convention update, i1 arguments/returns are assigned
to SGPRs without being promoted to i32. We need to update the
instruction selector to allow copy from physical reg to s1 destination.
---
 llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp b/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
index 03e2d622dd319..66b5beb3243be 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp
@@ -131,6 +131,16 @@ bool AMDGPUInstructionSelector::selectCOPY(MachineInstr &I) const {
   Register SrcReg = Src.getReg();
 
   if (isVCC(DstReg, *MRI)) {
+    // In planned update of calling convention, i1 arguments/returns are
+    // assigned to SGPRs without promoting to i32. The following if statement
+    // allows insturctions such as "%0:sreg_64_xexec(s1) = COPY $sgpr4_sgpr5"
+    // to be accepted.
+    if (SrcReg.isPhysical() && SrcReg != AMDGPU::SCC) {
+      const TargetRegisterClass *DstRC = MRI->getRegClassOrNull(DstReg);
+      if (DstRC)
+        return DstRC->contains(SrcReg);
+    }
+
     if (SrcReg == AMDGPU::SCC) {
       const TargetRegisterClass *RC
         = TRI.getConstrainedRegClassForOperand(Dst, *MRI);