shylie/llvm-project
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

[WebAssembly] Unstackify registers with no uses in ExplicitLocals (#149626)

Browse Source 
There are cases we end up removing some intructions that use stackified
registers after RegStackify. For example,

```wasm
bb.0:
  %0 = ...    ;; %0 is stackified
  br_if %bb.1, %0
bb.1:
```

In this code, br_if will be removed in CFGSort, so we should unstackify
%0 so that it can be correctly dropped in ExplicitLocals.

Rather than handling this in case-by-case basis, this PR just
unstackifies all stackifies register with no uses in the beginning of
ExplicitLocals, so that they can be correctly dropped.

Fixes #149097.

(cherry picked from commit b13bca7387a7aad6eaf3fa1c55bd06fe091f65ed)
This commit is contained in:
Heejin Ahn 2025-07-22 15:34:23 -07:00 committed by Tobias Hieta
parent 132d231605
commit dbe3ba0767
2 changed files with 36 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
View File

@ -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) {

26
llvm/test/CodeGen/WebAssembly/removed-terminator.ll Normal file
View File

@ -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
}