[llvm-branch-commits] [llvm] release 18.x: [ARM] Switch to LiveRegUnits to fix r7 register allocation bug (PR #84475)

[via llvm-branch-commits]

https://github.com/AtariDreams created https://github.com/llvm/llvm-project/pull/84475

This fixes a register allocation bug, because while r7 was marked as allowed to be used, LivePhysRegs always reported it as unavailable because it is reserved, despite this being an exception to the rule.

>From 99f0edf206aa40253db5feb3ea7d37d59ad715b5 Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Fri, 8 Mar 2024 07:59:02 -0500
Subject: [PATCH] [ARM] Switch to LiveRegUnits to fix r7 register allocation
 bug

This fixes a register allocation bug, because while r7 was marked as allowed to be used, LivePhysRegs always reported it as unavailable because it is reserved, despite this being an exception to the rule.
---
 llvm/lib/Target/ARM/Thumb1FrameLowering.cpp |  6 +++---
 llvm/test/CodeGen/Thumb/PR35481.ll          | 14 ++++++--------
 2 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp b/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp
index 0f4ece64bff532..a8cf036f363cdd 100644
--- a/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp
+++ b/llvm/lib/Target/ARM/Thumb1FrameLowering.cpp
@@ -612,11 +612,11 @@ bool Thumb1FrameLowering::needPopSpecialFixUp(const MachineFunction &MF) const {
 
 static void findTemporariesForLR(const BitVector &GPRsNoLRSP,
                                  const BitVector &PopFriendly,
-                                 const LivePhysRegs &UsedRegs, unsigned &PopReg,
+                                 const LiveRegUnits &UsedRegs, unsigned &PopReg,
                                  unsigned &TmpReg, MachineRegisterInfo &MRI) {
   PopReg = TmpReg = 0;
   for (auto Reg : GPRsNoLRSP.set_bits()) {
-    if (UsedRegs.available(MRI, Reg)) {
+    if (UsedRegs.available(Reg)) {
       // Remember the first pop-friendly register and exit.
       if (PopFriendly.test(Reg)) {
         PopReg = Reg;
@@ -684,7 +684,7 @@ bool Thumb1FrameLowering::emitPopSpecialFixUp(MachineBasicBlock &MBB,
   // Look for a temporary register to use.
   // First, compute the liveness information.
   const TargetRegisterInfo &TRI = *STI.getRegisterInfo();
-  LivePhysRegs UsedRegs(TRI);
+  LiveRegUnits UsedRegs(TRI);
   UsedRegs.addLiveOuts(MBB);
   // The semantic of pristines changed recently and now,
   // the callee-saved registers that are touched in the function
diff --git a/llvm/test/CodeGen/Thumb/PR35481.ll b/llvm/test/CodeGen/Thumb/PR35481.ll
index ad3215ecb94952..e48d1547782caf 100644
--- a/llvm/test/CodeGen/Thumb/PR35481.ll
+++ b/llvm/test/CodeGen/Thumb/PR35481.ll
@@ -18,11 +18,10 @@ define <4 x i32> @f() local_unnamed_addr #0 {
 ; CHECK-V4T-NEXT:    movs r2, #3
 ; CHECK-V4T-NEXT:    movs r3, #4
 ; CHECK-V4T-NEXT:    bl g
+; CHECK-V4T-NEXT:    ldr r7, [sp, #4]
+; CHECK-V4T-NEXT:    mov lr, r7
 ; CHECK-V4T-NEXT:    pop {r7}
-; CHECK-V4T-NEXT:    mov r12, r0
-; CHECK-V4T-NEXT:    pop {r0}
-; CHECK-V4T-NEXT:    mov lr, r0
-; CHECK-V4T-NEXT:    mov r0, r12
+; CHECK-V4T-NEXT:    add sp, #4
 ; CHECK-V4T-NEXT:    bx lr
 ;
 ; CHECK-V8M-LABEL: f:
@@ -36,11 +35,10 @@ define <4 x i32> @f() local_unnamed_addr #0 {
 ; CHECK-V8M-NEXT:    movs r1, #2
 ; CHECK-V8M-NEXT:    movs r2, #3
 ; CHECK-V8M-NEXT:    movs r3, #4
+; CHECK-V8M-NEXT:    ldr r7, [sp, #4]
+; CHECK-V8M-NEXT:    mov lr, r7
 ; CHECK-V8M-NEXT:    pop {r7}
-; CHECK-V8M-NEXT:    mov r12, r0
-; CHECK-V8M-NEXT:    pop {r0}
-; CHECK-V8M-NEXT:    mov lr, r0
-; CHECK-V8M-NEXT:    mov r0, r12
+; CHECK-V8M-NEXT:    add sp, #4
 ; CHECK-V8M-NEXT:    b g
 entry:
   %call = tail call i32 @h(i32 1)