[llvm] [MachineLICM] Clear subregister kill flags (PR #67240)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

<details>
<summary>Changes</summary>

When hosting a loop invariant instruction the resulting register must be live in
all the basic blocks of the loop body and the killed flags of the register must
be cleared.

Before this patch killed flags of subregister to a hoisted superregister was not
cleared in the loop body.

This was found in an out of tree target, but the testcase
mlicm-stack-write-check.mir was modified to trigger the case.


---
Full diff: https://github.com/llvm/llvm-project/pull/67240.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/MachineLICM.cpp (+1-1) 
- (modified) llvm/test/CodeGen/AArch64/mlicm-stack-write-check.mir (+35-2) 


``````````diff
diff --git a/llvm/lib/CodeGen/MachineLICM.cpp b/llvm/lib/CodeGen/MachineLICM.cpp
index fa7aa4a7a44ad08..6568b0aed799093 100644
--- a/llvm/lib/CodeGen/MachineLICM.cpp
+++ b/llvm/lib/CodeGen/MachineLICM.cpp
@@ -607,7 +607,7 @@ void MachineLICMBase::AddToLiveIns(MCRegister Reg) {
       for (MachineOperand &MO : MI.all_uses()) {
         if (!MO.getReg())
           continue;
-        if (TRI->isSuperRegisterEq(Reg, MO.getReg()))
+        if (TRI->regsOverlap(Reg, MO.getReg()))
           MO.setIsKill(false);
       }
     }
diff --git a/llvm/test/CodeGen/AArch64/mlicm-stack-write-check.mir b/llvm/test/CodeGen/AArch64/mlicm-stack-write-check.mir
index 276bd9fb269dc9f..0b1fdf9c33d66c6 100644
--- a/llvm/test/CodeGen/AArch64/mlicm-stack-write-check.mir
+++ b/llvm/test/CodeGen/AArch64/mlicm-stack-write-check.mir
@@ -17,11 +17,44 @@ body: |
   bb.1:
     ; CHECK-LABEL: bb.1:
     ; CHECK-NOT: $x2 = LDRXui %stack.0, 0
+    ; CHECK: $x0 = ADDXrr $x0, $x2
     liveins: $x0
     DBG_VALUE %stack.0, 0
     $x2 = LDRXui %stack.0, 0 :: (load (s64) from %stack.0)
-    $x0 = ADDXrr $x0, $x2
-    $xzr = SUBSXri $x0, 1, 0, implicit-def $nzcv
+    $x0 = ADDXrr $x0, killed $x2
+    $xzr = SUBSXri killed $x0, 1, 0, implicit-def $nzcv
+    Bcc 11, %bb.1, implicit $nzcv
+    B %bb.2
+
+  bb.2:
+    liveins: $x0
+    %0 = COPY $x0
+    %0 = COPY $x0  ; Force isSSA = false.
+...
+---
+name: test2
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: gpr64 }
+stack:
+  - { id: 0, size: 8, type: spill-slot }
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: test2
+    ; CHECK-LABEL: bb.0:
+    ; CHECK: $x2 = LDRXui %stack.0, 0
+    liveins: $x0, $x1, $x2
+    B %bb.1
+
+  bb.1:
+    ; CHECK-LABEL: bb.1:
+    ; CHECK-NOT: $x2 = LDRXui %stack.0, 0
+    ; CHECK: $w0 = ADDWrr $w0, $w2
+    liveins: $x0
+    DBG_VALUE %stack.0, 0
+    $x2 = LDRXui %stack.0, 0 :: (load (s64) from %stack.0)
+    $w0 = ADDWrr $w0, killed $w2
+    $wzr = SUBSWri killed $w0, 1, 0, implicit-def $nzcv
     Bcc 11, %bb.1, implicit $nzcv
     B %bb.2
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/67240