[Turbofan] Add concept of FP register aliasing on ARM 32.

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 5dfcbcc552c5c08844954d84412a380cbafa7a57..a41c93ca35cd4da655110c3ae73ce3c5029590f0 100644
--- a/src/compiler/wasm-linkage.cc
+++ b/src/compiler/wasm-linkage.cc
@@ -178,6 +178,17 @@ struct Allocator {
       // Allocate a floating point register/stack location.
       if (fp_offset < fp_count) {
         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),
+                        MachineTypeFor(type));
+        }
+#endif
         return regloc(reg, MachineTypeFor(type));
       } else {
         int offset = -1 - stack_offset;