[WebAssembly] Unstackify registers with no uses in ExplicitLocals #149626
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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, so that they can be correctly dropped. Fixes llvm#149097.
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@llvm/pr-subscribers-backend-webassembly Author: Heejin Ahn (aheejin) ChangesThere are cases we end up removing some intructions that use stackified registers after RegStackify. For example, 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, so that they can be correctly dropped. Fixes #149097. Full diff: https://github.com/llvm/llvm-project/pull/149626.diff 2 Files Affected:
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
index 2662241ef8499..ad28e36f29112 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 removes instructions that use 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..8c9b6ff4bca97
--- /dev/null
+++ b/llvm/test/CodeGen/WebAssembly/removed-terminator.ll
@@ -0,0 +1,14 @@
+; RUN: llc -O0 < %s
+
+target triple = "wasm32-unknown-unknown"
+
+define void @test(i1 %x) {
+ %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
+}
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nikic
reviewed
Jul 19, 2025
nikic
approved these changes
Jul 22, 2025
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/cherry-pick b13bca7 |
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/pull-request #150187 |
tru
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that referenced
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Jul 24, 2025
…vm#149626) 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 llvm#149097. (cherry picked from commit b13bca7)
mahesh-attarde
pushed a commit
to mahesh-attarde/llvm-project
that referenced
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Jul 28, 2025
…vm#149626) 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 llvm#149097.
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There are cases we end up removing some intructions that use stackified registers after RegStackify. For example,
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.