llvmbot wrote:

<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-webassembly

Author: None (llvmbot)

<details>
<summary>Changes</summary>

Backport b13bca7387a7aad6eaf3fa1c55bd06fe091f65ed

Requested by: @<!-- -->nikic

---
Full diff: https://github.com/llvm/llvm-project/pull/150187.diff


2 Files Affected:

- (modified) llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp (+10-2) 
- (added) llvm/test/CodeGen/WebAssembly/removed-terminator.ll (+26) 


``````````diff
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp 
b/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
index 2662241ef8499..e6486e247209b 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
@@ -256,9 +256,17 @@ bool 
WebAssemblyExplicitLocals::runOnMachineFunction(MachineFunction &MF) {
 
   // Precompute the set of registers that are unused, so that we can insert
   // drops to their defs.
+  // And unstackify any stackified registers that don't have any uses, so that
+  // they can be dropped later. This can happen when transformations after
+  // RegStackify remove instructions using stackified registers.
   BitVector UseEmpty(MRI.getNumVirtRegs());
-  for (unsigned I = 0, E = MRI.getNumVirtRegs(); I < E; ++I)
-    UseEmpty[I] = MRI.use_empty(Register::index2VirtReg(I));
+  for (unsigned I = 0, E = MRI.getNumVirtRegs(); I < E; ++I) {
+    Register Reg = Register::index2VirtReg(I);
+    if (MRI.use_empty(Reg)) {
+      UseEmpty[I] = true;
+      MFI.unstackifyVReg(Reg);
+    }
+  }
 
   // Visit each instruction in the function.
   for (MachineBasicBlock &MBB : MF) {
diff --git a/llvm/test/CodeGen/WebAssembly/removed-terminator.ll 
b/llvm/test/CodeGen/WebAssembly/removed-terminator.ll
new file mode 100644
index 0000000000000..188f6f67eee8b
--- /dev/null
+++ b/llvm/test/CodeGen/WebAssembly/removed-terminator.ll
@@ -0,0 +1,26 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py 
UTC_ARGS: --version 5
+; RUN: llc -O0 -verify-machineinstrs < %s | FileCheck %s
+
+target triple = "wasm32-unknown-unknown"
+
+define void @test(i1 %x) {
+; CHECK-LABEL: test:
+; CHECK:         .functype test (i32) -> ()
+; CHECK-NEXT:  # %bb.0:
+; CHECK-NEXT:    local.get 0
+; CHECK-NEXT:    i32.const -1
+; CHECK-NEXT:    i32.xor
+; CHECK-NEXT:    i32.const 1
+; CHECK-NEXT:    i32.and
+; CHECK-NEXT:    drop
+; CHECK-NEXT:  # %bb.1: # %exit
+; CHECK-NEXT:    return
+  %y = xor i1 %x, true
+  ; This br_if's operand (%y) is stackified in RegStackify. But this terminator
+  ; will be removed in CFGSort after that. We need to make sure we unstackify 
%y
+  ; so that it can be dropped in ExplicitLocals.
+  br i1 %y, label %exit, label %exit
+
+exit:
+  ret void
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/150187
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