[Turbofan] Add the concept of aliasing to RegisterConfiguration.

src/compiler/wasm-linkage.cc

Index: src/compiler/wasm-linkage.cc
diff --git a/src/compiler/wasm-linkage.cc b/src/compiler/wasm-linkage.cc
index 14d7e93d84cc029ea066bcc5194c599ca962a466..cfeb6c523f03d5f721d3b260858c82cc6cadc7ed 100644
--- a/src/compiler/wasm-linkage.cc
+++ b/src/compiler/wasm-linkage.cc
@@ -4,6 +4,7 @@
 
 #include "src/assembler.h"
 #include "src/macro-assembler.h"
+#include "src/register-configuration.h"
 
 #include "src/wasm/wasm-module.h"
 
@@ -178,7 +179,18 @@ struct Allocator {
     if (IsFloatingPoint(type)) {
       // Allocate a floating point register/stack location.
       if (fp_offset < fp_count) {
-        return regloc(fp_regs[fp_offset++]);
+        DoubleRegister reg = fp_regs[fp_offset++];
+#if V8_TARGET_ARCH_ARM
+        // Allocate floats using a double register, but modify the code to
+        // reflect how ARM FP registers alias.
+        // TODO(bbudge) Modify wasm linkage to allow use of all float regs.
+        if (type == kAstF32) {
+          int float_reg_code = reg.code() * 2;
+          DCHECK(float_reg_code < RegisterConfiguration::kMaxFPRegisters);
+          return regloc(DoubleRegister::from_code(float_reg_code));
+        }
+#endif
+        return regloc(reg);
       } else {
         int offset = -1 - stack_offset;
         stack_offset += Words(type);