fix floats in bailouts from POWER9 JIT project (branching adjust under separate investigation)

js/src/jit/JitFrames.cpp

@@ -1949,9 +1949,15 @@ SnapshotIterator::allocationValue(const RValueAllocation& alloc, ReadMethod rm)
         } pun;
         MOZ_ASSERT(alloc.fpuReg().isSingle());
         pun.d = fromRegister(alloc.fpuReg());
+#ifdef JS_CODEGEN_PPC_OSX
+        // The register is always written as a double, so we need to cast
+        // it down.
+        return Float32Value((float)pun.d);
+#else
         // The register contains the encoding of a float32. We just read
         // the bits without making any conversion.
         return Float32Value(pun.f);
+#endif
       }
 
       case RValueAllocation::ANY_FLOAT_STACK: