From 0f41b0708384c1f5d85304d5ed94d9edd57d38c9 Mon Sep 17 00:00:00 2001
From: Thomas Lively <7121787+tlively@users.noreply.github.com>
Date: Wed, 19 Dec 2018 19:22:09 -0800
Subject: Do not precompute v128 expressions (#1839)

Without this change, sequences like `i32.const 0, i32x4.splat` will
get precomputed to v128.const ops, which are much larger and also not
implemented in V8 yet. Until we have SIMD-aware optimization passes or
at least engine support for v128.const, do not perform such
transformations.
---
 src/passes/Precompute.cpp | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'src')

diff --git a/src/passes/Precompute.cpp b/src/passes/Precompute.cpp
index 9fb7ab31c..042a8be20 100644
--- a/src/passes/Precompute.cpp
+++ b/src/passes/Precompute.cpp
@@ -161,6 +161,10 @@ struct Precompute : public WalkerPass<PostWalker<Precompute, UnifiedExpressionVi
   void visitExpression(Expression* curr) {
     // TODO: if get_local, only replace with a constant if we don't care about size...?
     if (curr->is<Const>() || curr->is<Nop>()) return;
+    // Until engines implement v128.const and we have SIMD-aware optimizations
+    // that can break large v128.const instructions into smaller consts and
+    // splats, do not try to precompute v128 expressions.
+    if (curr->type == v128) return;
     // try to evaluate this into a const
     Flow flow = precomputeExpression(curr);
     if (flow.breaking()) {
-- 
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