[llvm] [SystemZ] Drop regstate of SELRMux operand in selectSLRMux(). (PR #128555)

[Jonas Paulsson via llvm-commits]

https://github.com/JonPsson1 created https://github.com/llvm/llvm-project/pull/128555

It seems that there can be other cases with this that also can lead to wrong code (discovered with csmith). This time it involved not the kill flag but the undef flag.

It seems safest then to drop all the flags except for the renamable flag, which should always be true.



>From c1db6a61c97872a792d1ddcc1d8c0541d4971194 Mon Sep 17 00:00:00 2001
From: Jonas Paulsson <paulson1 at linux.ibm.com>
Date: Mon, 24 Feb 2025 19:42:34 +0100
Subject: [PATCH] Drop regstate of SELRMux operand.

---
 .../lib/Target/SystemZ/SystemZPostRewrite.cpp |  2 +-
 llvm/test/CodeGen/SystemZ/cond-move-10.mir    |  2 +-
 llvm/test/CodeGen/SystemZ/cond-move-11.mir    | 43 +++++++++++++++++++
 3 files changed, 45 insertions(+), 2 deletions(-)
 create mode 100644 llvm/test/CodeGen/SystemZ/cond-move-11.mir

diff --git a/llvm/lib/Target/SystemZ/SystemZPostRewrite.cpp b/llvm/lib/Target/SystemZ/SystemZPostRewrite.cpp
index cf3073f0f2090..74c270f1c5018 100644
--- a/llvm/lib/Target/SystemZ/SystemZPostRewrite.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZPostRewrite.cpp
@@ -114,7 +114,7 @@ void SystemZPostRewrite::selectSELRMux(MachineBasicBlock &MBB,
   if (Src1Reg == Src2Reg) {
     BuildMI(*MBBI->getParent(), MBBI, MBBI->getDebugLoc(),
             TII->get(SystemZ::COPY), DestReg)
-        .addReg(MBBI->getOperand(1).getReg(), getRegState(MBBI->getOperand(1)));
+        .addReg(MBBI->getOperand(1).getReg(), RegState::Renamable);
     MBBI->eraseFromParent();
     return;
   }
diff --git a/llvm/test/CodeGen/SystemZ/cond-move-10.mir b/llvm/test/CodeGen/SystemZ/cond-move-10.mir
index 1db960829729e..7a27d8b02271f 100644
--- a/llvm/test/CodeGen/SystemZ/cond-move-10.mir
+++ b/llvm/test/CodeGen/SystemZ/cond-move-10.mir
@@ -5,7 +5,7 @@
 # CHECK:      name: fun0
 # CHECK:      renamable $r1l = AHIMuxK killed renamable $r1l, -1, implicit-def dead $cc
 # CHECK-NEXT: CHIMux renamable $r5h, 9, implicit-def $cc
-# CHECK-NEXT: $r14h = COPY killed renamable $r1l
+# CHECK-NEXT: $r14h = COPY renamable $r1l
 ---
 name:            fun0
 tracksRegLiveness: true
diff --git a/llvm/test/CodeGen/SystemZ/cond-move-11.mir b/llvm/test/CodeGen/SystemZ/cond-move-11.mir
new file mode 100644
index 0000000000000..a2431d9466fd1
--- /dev/null
+++ b/llvm/test/CodeGen/SystemZ/cond-move-11.mir
@@ -0,0 +1,43 @@
+# RUN: llc -o - %s -mtriple=s390x-linux-gnu -mcpu=z15 -start-before=systemz-post-rewrite \
+# RUN:   -stop-after=machine-cp 2>&1 | FileCheck %s
+
+# The chained SELRMux:es both has two operands with the same register but
+# where one of the operands have been marked as undef (resulting from
+# early-ifcvt). Check that the resulting COPY after machine-cp is from $r0l
+# to $r2l.
+
+# CHECK:      name: fun0
+# CHECK:      $r2l = COPY $r0l
+--- |
+  
+  @Res = global i32 0, align 4
+  @Z = global i32 0, align 4
+  define signext i32 @fun0() { ret i32 0 }
+...
+---
+name:            fun0
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    successors: %bb.1(0x80000000)
+  
+    renamable $r0l = LRL @Z :: (dereferenceable load (s32) from @Z)
+    renamable $r1l = LHIMux 1
+  
+  bb.1:
+    successors: %bb.1(0x7c000000), %bb.2(0x04000000)
+    liveins: $r0l, $r1l
+  
+    CHIMux renamable $r1l, 0, implicit-def $cc
+    renamable $r2l = SELRMux undef renamable $r0l, renamable $r0l, 14, 6, implicit $cc
+    renamable $r2l = SELRMux undef renamable $r2l, killed renamable $r2l, 14, 6, implicit $cc
+    BRC 14, 8, %bb.1, implicit killed $cc
+    J %bb.2
+  
+  bb.2:
+    liveins: $r2l
+  
+    STRL renamable $r2l, @Res :: (store (s32) into @Res)
+    renamable $r2d = LGFR killed renamable $r2l
+    Return implicit $r2d
+...