[llvm] [Thumb1] Resolve Fixme: use 'mov hi, $src; mov $dst, hi' (PR #81908)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-arm

Author: AtariDreams (AtariDreams)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/81908.diff


1 Files Affected:

- (modified) llvm/lib/Target/ARM/Thumb1InstrInfo.cpp (+29-3) 


``````````diff
diff --git a/llvm/lib/Target/ARM/Thumb1InstrInfo.cpp b/llvm/lib/Target/ARM/Thumb1InstrInfo.cpp
index 85eabdb17ad190..01b8c76674d207 100644
--- a/llvm/lib/Target/ARM/Thumb1InstrInfo.cpp
+++ b/llvm/lib/Target/ARM/Thumb1InstrInfo.cpp
@@ -53,9 +53,6 @@ void Thumb1InstrInfo::copyPhysReg(MachineBasicBlock &MBB,
         .addReg(SrcReg, getKillRegState(KillSrc))
         .add(predOps(ARMCC::AL));
   else {
-    // FIXME: Can also use 'mov hi, $src; mov $dst, hi',
-    // with hi as either r10 or r11.
-
     const TargetRegisterInfo *RegInfo = st.getRegisterInfo();
     if (MBB.computeRegisterLiveness(RegInfo, ARM::CPSR, I)
         == MachineBasicBlock::LQR_Dead) {
@@ -65,6 +62,35 @@ void Thumb1InstrInfo::copyPhysReg(MachineBasicBlock &MBB,
       return;
     }
 
+    // Can also use 'mov hi, $src; mov $dst, hi',
+    // with hi as either r10 or r11.
+    if (MBB.computeRegisterLiveness(RegInfo, ARM::R10, I) ==
+        MachineBasicBlock::LQR_Dead) {
+      // Use high register to move source to destination
+      BuildMI(MBB, I, DL, get(ARM::tMOVr), ARM::R10)
+          .addReg(SrcReg, getKillRegState(KillSrc))
+          .add(predOps(ARMCC::AL));
+      BuildMI(MBB, I, DL, get(ARM::tMOVr), DestReg)
+          .addReg(ARM::R10, getKillRegState(KillSrc))
+          .add(predOps(ARMCC::AL))
+          ->addRegisterDead(ARM::R10, RegInfo);
+      return;
+    }
+
+    if (MBB.computeRegisterLiveness(RegInfo, ARM::R11, I) ==
+        MachineBasicBlock::LQR_Dead) {
+      // Use high register to move source to destination
+      BuildMI(MBB, I, DL, get(ARM::tMOVr), ARM::R11)
+          .addReg(SrcReg, getKillRegState(KillSrc))
+          .add(predOps(ARMCC::AL));
+      BuildMI(MBB, I, DL, get(ARM::tMOVr), DestReg)
+          .addReg(ARM::R11, getKillRegState(KillSrc))
+          .add(predOps(ARMCC::AL))
+          ->addRegisterDead(ARM::R11, RegInfo);
+      ;
+      return;
+    }
+
     // 'MOV lo, lo' is unpredictable on < v6, so use the stack to do it
     BuildMI(MBB, I, DL, get(ARM::tPUSH))
         .add(predOps(ARMCC::AL))

``````````

</details>


https://github.com/llvm/llvm-project/pull/81908