[llvm-branch-commits] [llvm] release/21.x: [WebAssembly] Unstackify registers with no uses in ExplicitLocals (#149626) (PR #150187)
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Wed Jul 23 01:34:42 PDT 2025
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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