Revert "[wasm] Use 64-bit comparison for bounds checks on 64-bit platforms"

This reverts commit 972d460f.

Reason for revert: This CL is not the right solution, and it makes back-merging the right solution more difficult.

Original change's description:
> [wasm] Use 64-bit comparison for bounds checks on 64-bit platforms
> 
> By using 64-bit comparison we make sure that there will be no out of
> memory accesses even if there are stale values in the high word of a
> register.
> 
> R=​titzer@chromium.org
> 
> Change-Id: I2627b15e1598f35cc480d7028031e8de405164ea
> Reviewed-on: https://chromium-review.googlesource.com/721323
> Reviewed-by: Ben Titzer <titzer@chromium.org>
> Commit-Queue: Andreas Haas <ahaas@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#48604}

TBR=titzer@chromium.org,ahaas@chromium.org

Change-Id: I0c15e9d8ac72def2e22543a17366126d90a17918
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/721702Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48628}

src/compiler/wasm-compiler.cc

@@ -3405,9 +3405,10 @@ void WasmGraphBuilder::BoundsCheckMem(MachineType memtype, Node* index,
     // The end offset is larger than the smallest memory.
     // Dynamically check the end offset against the actual memory size, which
     // is not known at compile time.
-    Node* cond =
-        graph()->NewNode(jsgraph()->machine()->Uint32LessThanOrEqual(),
-                         jsgraph()->Int32Constant(end_offset), *mem_size_);
+    Node* cond = graph()->NewNode(
+        jsgraph()->machine()->Uint32LessThanOrEqual(),
+        jsgraph()->IntPtrConstant(static_cast<uintptr_t>(end_offset)),
+        *mem_size_);
     TrapIfFalse(wasm::kTrapMemOutOfBounds, cond, position);
   } else {
     // The end offset is within the bounds of the smallest memory, so only
@@ -3427,10 +3428,8 @@ void WasmGraphBuilder::BoundsCheckMem(MachineType memtype, Node* index,
       graph()->NewNode(jsgraph()->machine()->Int32Sub(), *mem_size_,
                        jsgraph()->Int32Constant(end_offset - 1));
 
-  const Operator* less = jsgraph()->machine()->Is32()
-                             ? jsgraph()->machine()->Uint32LessThan()
-                             : jsgraph()->machine()->Uint64LessThan();
-  Node* cond = graph()->NewNode(less, index, effective_size);
+  Node* cond = graph()->NewNode(jsgraph()->machine()->Uint32LessThan(), index,
+                                effective_size);
   TrapIfFalse(wasm::kTrapMemOutOfBounds, cond, position);
 }