From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Zhi An Ng <zhin@chromium.org>
Date: Fri, 8 Jan 2021 07:29:02 +0000
Subject: Merged: [wasm-simd] Fix loading fp pair registers

We were incorrectly clearing the high reg from the list of regs to load.
The intention was to prevent double (and incorrect) loading - loading
128 bits from the low fp and the loading 128 bits from the high fp.
But this violates the assumption that the two regs in a pair would be
set or unset at the same time.

The fix here is to introduce a new enum for register loads, a nop, which
does nothing. The high fp of the fp pair will be tied to this nop, so as
we iterate down the reglist, we load 128 bits using the low fp, then
don't load anything for the high fp.

Bug: chromium:1161654
(cherry picked from commit 8c698702ced0de085aa91370d8cb44deab3fcf54)

Change-Id: Ib8134574b24f74f24ca9efd34b3444173296d8f1
No-Try: true
No-Presubmit: true
No-Tree-Checks: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2619416
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/branch-heads/8.8@{#28}
Cr-Branched-From: 2dbcdc105b963ee2501c82139eef7e0603977ff0-refs/heads/8.8.278@{#1}
Cr-Branched-From: 366d30c99049b3f1c673f8a93deb9f879d0fa9f0-refs/heads/master@{#71094}

diff --git a/src/wasm/baseline/liftoff-assembler.cc b/src/wasm/baseline/liftoff-assembler.cc
index 74df00590ff77377321092a3a2a51fb52154e5cf..acc4896d02782a9faccb5d91ab04d9d2603bbd44 100644
--- a/src/wasm/baseline/liftoff-assembler.cc
+++ b/src/wasm/baseline/liftoff-assembler.cc
@@ -36,6 +36,7 @@ class StackTransferRecipe {
 
   struct RegisterLoad {
     enum LoadKind : uint8_t {
+      kNop,           // no-op, used for high fp of a fp pair.
       kConstant,      // load a constant value into a register.
       kStack,         // fill a register from a stack slot.
       kLowHalfStack,  // fill a register from the low half of a stack slot.
@@ -62,6 +63,10 @@ class StackTransferRecipe {
       return {half == kLowWord ? kLowHalfStack : kHighHalfStack, kWasmI32,
               offset};
     }
+    static RegisterLoad Nop() {
+      // ValueType does not matter.
+      return {kNop, kWasmI32, 0};
+    }
 
    private:
     RegisterLoad(LoadKind kind, ValueType type, int32_t value)
@@ -216,11 +221,11 @@ class StackTransferRecipe {
           RegisterLoad::HalfStack(stack_offset, kHighWord);
     } else if (dst.is_fp_pair()) {
       DCHECK_EQ(kWasmS128, type);
-      // load_dst_regs_.set above will set both low and high fp regs.
-      // But unlike gp_pair, we load a kWasm128 in one go in ExecuteLoads.
-      // So unset the top fp register to skip loading it.
-      load_dst_regs_.clear(dst.high());
+      // Only need register_load for low_gp since we load 128 bits at one go.
+      // Both low and high need to be set in load_dst_regs_ but when iterating
+      // over it, both low and high will be cleared, so we won't load twice.
       *register_load(dst.low()) = RegisterLoad::Stack(stack_offset, type);
+      *register_load(dst.high()) = RegisterLoad::Nop();
     } else {
       *register_load(dst) = RegisterLoad::Stack(stack_offset, type);
     }
@@ -317,6 +322,8 @@ class StackTransferRecipe {
     for (LiftoffRegister dst : load_dst_regs_) {
       RegisterLoad* load = register_load(dst);
       switch (load->kind) {
+        case RegisterLoad::kNop:
+          break;
         case RegisterLoad::kConstant:
           asm_->LoadConstant(dst, load->type == kWasmI64
                                       ? WasmValue(int64_t{load->value})
diff --git a/test/mjsunit/regress/wasm/regress-1161654.js b/test/mjsunit/regress/wasm/regress-1161654.js
new file mode 100644
index 0000000000000000000000000000000000000000..93f2c3b556fc55edc157dadc49b23d5bc9538135
--- /dev/null
+++ b/test/mjsunit/regress/wasm/regress-1161654.js
@@ -0,0 +1,56 @@
+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --wasm-staging
+
+// This is a fuzzer-generated test case that exposed a bug in Liftoff that only
+// affects ARM, where the fp register aliasing is different from other archs.
+// We were inncorrectly clearing the the high fp register in a LiftoffRegList
+// indicating registers to load, hitting a DCHECK.
+load('test/mjsunit/wasm/wasm-module-builder.js');
+
+const builder = new WasmModuleBuilder();
+builder.addMemory(19, 32, false);
+builder.addGlobal(kWasmI32, 0);
+builder.addType(makeSig([], []));
+builder.addType(makeSig([kWasmI64, kWasmS128, kWasmF32], [kWasmI32]));
+// Generate function 1 (out of 5).
+builder.addFunction(undefined, 0 /* sig */)
+  .addBodyWithEnd([
+// signature: v_v
+// body:
+kExprI32Const, 0x05,  // i32.const
+kExprReturn,  // return
+kExprUnreachable,  // unreachable
+kExprEnd,  // end @5
+]);
+// Generate function 4 (out of 5).
+builder.addFunction(undefined, 1 /* sig */)
+  .addBodyWithEnd([
+// signature: i_lsf
+// body:
+kExprLocalGet, 0x01,  // local.get
+kExprLocalGet, 0x01,  // local.get
+kExprGlobalGet, 0x00,  // global.get
+kExprDrop,  // drop
+kExprLoop, kWasmStmt,  // loop @8
+  kExprLoop, 0x00,  // loop @10
+    kExprI32Const, 0x01,  // i32.const
+    kExprMemoryGrow, 0x00,  // memory.grow
+    kExprI64LoadMem8U, 0x00, 0x70,  // i64.load8_u
+    kExprLoop, 0x00,  // loop @19
+      kExprCallFunction, 0x00,  // call function #0: v_v
+      kExprEnd,  // end @23
+    kExprI64Const, 0xf1, 0x24,  // i64.const
+    kExprGlobalGet, 0x00,  // global.get
+    kExprDrop,  // drop
+    kExprBr, 0x00,  // br depth=0
+    kExprEnd,  // end @32
+  kExprEnd,  // end @33
+kExprI32Const, 0x5b,  // i32.const
+kExprReturn,  // return
+kExprEnd,  // end @37
+]);
+// Instantiation is enough to cause a crash.
+const instance = builder.instantiate();
