Fix corner cases for double pow operation.

runtime/vm/intermediate_language_mips.cc

Index: runtime/vm/intermediate_language_mips.cc
===================================================================
--- runtime/vm/intermediate_language_mips.cc	(revision 26658)
+++ runtime/vm/intermediate_language_mips.cc	(working copy)
@@ -3524,6 +3524,8 @@
 
 
 LocationSummary* InvokeMathCFunctionInstr::MakeLocationSummary() const {
+  // Calling convetion on MIPS uses D6 and D7 to pass the first two
+  // double arguments.
   ASSERT((InputCount() == 1) || (InputCount() == 2));
   const intptr_t kNumTemps = 0;
   LocationSummary* result =
@@ -3541,11 +3543,39 @@
   // For pow-function return NaN if exponent is NaN.
   Label do_call, skip_call;
   if (recognized_kind() == MethodRecognizer::kMathDoublePow) {
+    // Pseudo code:
+    // if (exponent == 0.0) return 0.0;
+    // if (base == 1.0) return 1.0;
+    // if (base.isNaN || exponent.isNaN) {
+    //    return double.NAN;
+    // }
+    DRegister base = locs()->in(0).fpu_reg();
     DRegister exp = locs()->in(1).fpu_reg();
+    DRegister result = locs()->out().fpu_reg();
+
+    Label check_base_is_one;
+
+    // Check if exponent is 0.0 -> return 1.0;
+    __ LoadObject(TMP, Double::ZoneHandle(Double::NewCanonical(0)));
+    __ LoadDFromOffset(DTMP, TMP, Double::value_offset() - kHeapObjectTag);
+    __ LoadObject(TMP, Double::ZoneHandle(Double::NewCanonical(1)));
+    __ LoadDFromOffset(result, TMP, Double::value_offset() - kHeapObjectTag);
+    // 'result' contains 1.0.
     __ cund(exp, exp);
-    __ bc1f(&do_call);
-    // Exponent is NaN, return NaN.
-    __ movd(locs()->out().fpu_reg(), exp);
+    __ bc1t(&check_base_is_one);  // NaN -> not zero.
+    __ ceqd(exp, DTMP);
+    __ bc1t(&skip_call);  // exp is 0.0, result is 1.0.
+
+    Label base_is_nan;
+    __ Bind(&check_base_is_one);
+    __ cund(base, base);
+    __ bc1t(&base_is_nan);
+    __ ceqd(base, result);
+    __ bc1t(&skip_call);  // base and result are 1.0.
+    __ b(&do_call);
+
+    __ Bind(&base_is_nan);
+    __ movd(result, base);  // base is NaN, return NaN.
     __ b(&skip_call);
   }
   __ Bind(&do_call);