check if we can split (linear scan)

Revert "[wasm] Quickfix for register allocation problem on ia32."

This reverts commit 2ca31b63.

BUG=

Review URL: https://codereview.chromium.org/1824303002

Cr-Commit-Position: refs/heads/master@{#35559}

src/compiler/register-allocator.cc

@@ -2947,9 +2947,13 @@ void LinearScanAllocator::AllocateBlockedReg(LiveRange* current) {
   LifetimePosition pos = use_pos[reg];
 
   if (pos < register_use->pos()) {
-    // All registers are blocked before the first use that requires a register.
-    // Spill starting part of live range up to that use.
-    SpillBetween(current, current->Start(), register_use->pos());
+    if (LifetimePosition::ExistsGapPositionBetween(current->Start(),
+                                                   register_use->pos())) {
+      SpillBetween(current, current->Start(), register_use->pos());
+    } else {
+      SetLiveRangeAssignedRegister(current, reg);
+      SplitAndSpillIntersecting(current);
+    }
     return;
   }
 
@@ -2994,6 +2998,8 @@ void LinearScanAllocator::SplitAndSpillIntersecting(LiveRange* current) {
         // live-ranges: ranges are allocated in order of their start positions,
         // ranges are retired from active/inactive when the start of the
         // current live-range is larger than their end.
+        DCHECK(LifetimePosition::ExistsGapPositionBetween(current->Start(),
+                                                          next_pos->pos()));
         SpillBetweenUntil(range, spill_pos, current->Start(), next_pos->pos());
       }
       ActiveToHandled(range);

src/compiler/register-allocator.h

@@ -46,6 +46,14 @@ class LifetimePosition final {
     return LifetimePosition(index * kStep + kHalfStep);
   }
 
+  static bool ExistsGapPositionBetween(LifetimePosition pos1,
+                                       LifetimePosition pos2) {
+    if (pos1 > pos2) std::swap(pos1, pos2);
+    LifetimePosition next(pos1.value_ + 1);
+    if (next.IsGapPosition()) return next < pos2;
+    return next.NextFullStart() < pos2;
+  }
+
   // Returns a numeric representation of this lifetime position.
   int value() const { return value_; }
 

src/compiler/wasm-linkage.cc

@@ -58,7 +58,7 @@ LinkageLocation stackloc(int i) {
 // ===========================================================================
 // == ia32 ===================================================================
 // ===========================================================================
-#define GP_PARAM_REGISTERS eax, edx, ecx, ebx
+#define GP_PARAM_REGISTERS eax, edx, ecx, ebx, esi
 #define GP_RETURN_REGISTERS eax, edx
 #define FP_PARAM_REGISTERS xmm1, xmm2, xmm3, xmm4, xmm5, xmm6
 #define FP_RETURN_REGISTERS xmm1, xmm2